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lould be retoraea^n^?&8orc ^Vic'last marked b<flo 

Popular Gemology 

Oriental Figure Carved in lu'^rirri A- 

[Fron, .Yard's X-,ir* c.\ 

Popular tiemology 

Ilirlicird M. Pearl 


John Wiley & Sons, liu 1 ., New York 

ii X- H.ill Ltd., London 1948 



All Rights Reserved 

This book or any part thereof mmt not 
be reproduced in any form without 
the written permission of the publisher. 

Dedicated with affection 

to my wife's mother, 
Align on Preston War dell 


This book is intended to present in popular language for 
the general reader the most recent accurate knowledge 
about the world of gems. It was planned to fulfill the 
need for a semi-technical survey of modern gemology 
simplified, authoritative, and up-to-date. It is written for 
the gem lover, the mineral collector, the jeweler, and the 

Completed since the war, Popular Gemology is timed 
to include the new scientific and industrial uses of gems, 
both natural and artificial, as well as the most recent de- 
velopments in commerce brought about by the Avar, and 
current locality and production information. 

A systematic arrangement of subject matter has been 
attempted throughout. The chapters describing the indi- 
vidual gems have been divided primarily according to the 
major style of cutting (facet or cabochon) which is gen- 
erally^ most appropriate for each gem; the cutting in turn 
depends upon the inherent characteristics of the gem and 
so fits into a logical yet original grouping. 

-in the chapters the order of gems, with only a few 
le exceptions, follows the best scientific classifi- 
minerals, that given in the seventh edition of 
of Mineralogy / two of the three volumes 

chc, Bcrnian, and Frondel, Harvard University. Published by 
Ar;i and Sons, Inc., New York. Volume 


of which are unpublished. This sequence is surely su- 
perior to a meaningless alphabetic listing or the usual 
arrangement by value, which is always subject to personal 
interpretation. Diamond, by fortunate coincidence, occu- 
pies the first position in either a commercial or a scientific 
succession. Emphasis has been placed consistently on the 
mineral family, series, and species as the natural units. 
Careful attention has been devoted to nomenclature, in 
order that no technical word should be employed in a 
wrong sense to simplify its use. 

Popular Gevwlogy was conceived in Oregon, begun in 
Tulsa, Oklahoma, continued in Denver, Colorado, and 
Cambridge, Massachusetts, and completed in Colorado 
Springs. It was undertaken at the suggestion of Dr. Henry 
C. Dake of Portland, editor of The Mineralogist^ who was 
to have been co-author but was obliged to withdraw under 
the pressure of business. In addition to the idea, Dr. Dake 
contributed the title, the chief basis of classification accord- 
ing to type of cutting, and many of the photographs. For 
all this assistance and encouragement I am deeply in his 
debt. Acknowledgment should also be made to the other 
individuals, educational institutions, and industrial firms 
that furnished photographs; their names are printed at the 
proper places in the book. My personal thanks go to Pro- 
fessor Edna D. Romig of the University of Colorado for 
assistance in a number of the more subtle points of compo- 
sition; and to my wife, Mignon, for her continued co- 
operation in every phase of the work, ranging from - ,, 
to the actual invention of several of the impor 

of the book. ^ ., v 


Colorado Springs 




Birtbstones, 4 


The Nature of Geins, 6; Cbewistry of Gems, 11; 
Gem Crystals, 15; Optical Properties of Gems, 24; 
Physical Properties of Gems, 5 1 ; Occurrence of 
Gems, 65 


Dinosaurs to Dynasties: The Story of Diamond, 75; 
Corundum, 98; Spinel, 104; Chrysoberyl, 107; Sphal- 
erite, 111; Cassiterite, 112; Fluorite, 112; Erazilianite, 
114; Apatite, 115; Scapolite, 116; Cordierite, 117; ;/- 
statite, 118; Diopside, 119; Spodumene, 120; Eenitoite, 
122; Tounmline, 124; Eery I, 131; Danbitrite, 137; 
OH vine, 138; Pbenakite, 140; Willemite, 140; Garnet, 
141; Epidote, 147; Zircon, 148; Datolite, 154; Euclase, 
154; TO/MS, 155; Axinite, 158; Andalushe, 158; S/7/i- 
manlte, 159; Kyanite, 160; Sphene, 161 


Metallic Gems, 164; Noirmetallic Cabochon and 
ved Gems, 167; Ornamental Stones, 198 


//K/YZ, 203; Chalcedony, 212; Opd?/, 224; Natural 
Ihiss, 229 




Pearl y 233; Coral, 238; Amber, 240; Jet, 244 


'Synthetic Gems, 248; Imitation Gems, 259; Composite 
Gems, 263; Treated Gems, 265; Cultured Pearl, 266 


Fluorescent Equipment, 278 


INDEX 287 


Chapter 1 

The Lure of Gems 

The fascination which gems have always held for men 
and women goes beyond the shadowy dawn of antiq- 
uity to the very beginnings of the human race. Its origin 
must lie in stages of development even antedating man- 
kind; for a bird will pick up bits of brightly colored 
twigs and twine in preference to more somber ones with 
which to build its nest, as we choose objects to ornament 
our clothing or our person. 

Whether gems as personal adornment preceded or 
were subsequent to gems as amulets and charms is de- 
batable. It was easy for primitive peoples to ascribe super- 
natural powers to especially attractive or otherwise unusual 
stones that they found in the beds of streams, on the slopes 
of hills, and on the rocky floors of the hospitable caves 
where they sought shelter from inclement weather or un- 
friendly animals. Whichever came first, ornament or 
talisman, the benefits of both were soon combined in the 

solution of jewelry forms parallels the progress 
! apidary art. Earliest of all articles of jewelry was 
the necklace. At first, roagh pebbles were 

merely drilled and strung, but refined techniques led by 
steps to the rounding and then to the polishing of the 
natural shapes, although crystal faces were often carefully 
preserved. From the stringing of necklaces to the. making 
of bracelets was a close transition, since beads were used 
for both. The introduction of the gem-set metal bracelet 
and the invention of the ring awaited a more advanced 

Amulets whose purpose as such is undeniable were pro- 
duced from gems and common stones by marking them 
with prayers and images. The inhabitants of Babylonia, 
Assyria and Persia carved such inscriptions and figures 
into long beads called cylinders, which were pierced 
lengthwise for wearing. These were also used as seals. 
At about the time of the 9th dynasty in Egypt the scarab 
became prominent in art; this is a representation of a 
beetle, symbol of the immortality of the soul, and was 
employed for both seals and amulrts. 

Not least among the achievements of Greek and Roman 
artists was their gem engraving. Exquisite craftsmanship 
was encouraged by the high value and small size of the 
material at their disposal. The superior durability of most 
gemstones has made possible their remarkable preservation 
through succeeding centuries, so that even today we see 
the gems essentially as they appeared to the original owner. 
Furthermore, a pageant of classic art in miniature is re- 
vealed, showing accurately its struggle for recognition, its 
Golden Age, and its eventual decadence. 

As the variety of designs expanded and the treatmen** 
became more personalized and naturalistic, the number < 
gems regularly used increased. A notable improve ii> 
was the introduction of the cameo about ?00 tf.c 

design being carved in relief for decorative purposes only, 
in Contrast to the older form called the intaglio, in which 
the design was incised into the surface of the gem to serve 
most faithfully as a signet in those not-too-literate days. 

After the classic era, the art of gem engraving declined, 
to be revived with new spirit in the Renaissance and 
again, with far less originality, in the 1 8th century. Present- 
day gem carving, though still done with hand tools, is on 
a more commercial basis. 

A love of gems characterizes all races and all social levels. 
There have been few famous persons in history who have 
not been traditionally identified with a particular gem. 
Private and public collections have been diligently as- 
sembled. In Rome wealthy families competed with one 
another in acquiring choice gems and displaying them in 
the temples. 

The medical or therapeutic use of gems is as varied as 
the gems themselves. Any disease of man or beast was 
believed to be preventable or curable by swallowing the 
powder of the proper gems, chosen for their color or chem- 
ical ingredients, or by applying them whole. Strong and 
no doubt often fatal potions were prescribed on any occa- 
sion. Some of these superstitions linger to the present time; 
necklaces of amber, for instance, are still bought in Ameri- 
can stores as a remedy for goiter. 

The symbolism of gems ranges from the charming to 

the bizarre and to the merely ridiculous. As the mystical 

and religious attributes of gems are compared, it becomes 

evident that at one time or another almost all the virtues 

ive been ascribed to almost every gem. Formerly, the 

\y of gems was dominated by this aspect of the subject, 

-Ke growth of modern science has dispelled much 


of the ignorance, if not the entire fantasy, surrounding 
gems, and gem lore has largely yielded to gemology. 
What were once exclusively trade secrets, guarded jeal- 
ously and handed down from father to son, have now 
become the possession of every person who cares to read 
and learn. 

The gemological movement began in Europe. The 
Gemmological Association of Great Britain was estab- 
lished in London in 1913 as an adjunct of the National 
Association of Goldsmiths of Great Britain and Ireland. 
Patterned after it but now greatly expanded in scope is 
the Gemological Institute of America, founded in Los 
Angeles in 1931 by Robert M. Shipley; it conducts courses, 
principally for members of the jewelry industry. An 
affiliated organization is the American Gem Society, the 
activities of which are directed toward the education of 
the trade and the protection of the public; the title Certi- 
fied Gewologist is its highest award. Similar associations 
are being started in other countries, the newest ones being 
the Gemmological Association of Australia (1946) and 
national groups in Sweden and Switzerland. 


The pleasant custom of wearing a special gem that be- 
longs to the month in which one was born seems to have 
had its origin in Germany or Poland during the 16th cen- 
tury. The arrangement probably corresponded at f : x> 
the signs of the zodiac rather than to the calendai 
This idea can be traced back to the twelve h 
stones of the holy city, New Jerusalem, dcsc-.ibt 
21st chapter of the Book of Revelation or the -ty 


Each of the stones was inscribed with the name of an 
apostle. The direct predecessor of the New Testament list 
was a different series, consisting of the twelve gems (each 
engraved with the name of one of the tribes of Israel) 
which adorned the breastplate of judgment worn by the 
high priest and described in Exodus 28. 

The names of all these gems are not always identical in 
the several lists that appear in the Bible and other writings; 
discrepancies may be accounted for by changes in the 
actual breastplate, difficulties in manuscript translation, 
errors in copying, and inability to identify certain stones 
by their descriptions. Different races and nations have had 
their favorite birthstoncs; a composite selection, partly tra- 
ditional and partly arbitrary, constitutes the list of natal 
gems conventionally sold in the United States. Alternate 
selections of gems have been recommended according to 
the apostles, guardian angels, zodiacal signs, days of the 
week, hours of the day, and assorted ideas without end; all 
of them serve the purpose of supplying a reason for buying 
a gem which the purchaser usually wants to buy anyway 
and for wearing a gem which the owner is perfectly willing 
to wear without apology. We may prefer to believe with 
Emerson that "Beauty is its own excuse for being" and a 
gem for being worn. 

Chapter 2 

Recognizing Gems 

The art and science of gemology deals with certain nat- 
ural substances and their man-made substitutes, which 
human beings regard as attractive enough to serve primarily 
for personal adornment and secondarily for decoration of 
their possessions. A gem becomes a jewel when it is placed 
in a setting appropriate to its use. 


Most gems are minerals. A mineral is defined as a 
homogeneous substance produced by inorganic processes, 
and occurring in nature with a specific chemical compo- 
sition; it usually has a definite internal structure which 
may be expressed in typical outward forms called crystals. 

A substance is homogeneous when it is uniform even 
under a microscope; this requirement excludes rocks, some 
of which appear to be the same throughout but are found 
upon close examination to be aggregates of several different- 
materials. Products of animal or vegetable life are b?~ 
because they are not inorganic. Manufactured che 
are not embraced among the minerals because they d 


occur in nature. The chemical composition of a mineral 
must be represented by a formula or else be variable 
according to a dependable law. A definite internal struc- 
ture implies a three-dimensional pattern of atoms (as shown 

Fig. 1 Atomic Structure of Diamond 
[From Dana-Ford A Textbook of Mineralogy, copyright 1932.] 

in Fig. 1), the arrangement of which is intimately related 
to the crystal form and to other essential characters. 

About 80 of the 1,000 or more mineral species have been 

regarded as gems, though many of these are met with only 

occasionally. Diamond, the noblest of gems, is perhaps 

the mo& remarkable of all minerals. 

A few gettis are rocks. Members of the so-called min- 

1 kingdom that fail to satisfy the fairly strict require- 

of a mineral are termed rocks. Basically, a rock is 

nass that forms an important part of the earth. It 

may be a single mineral such as salt, or a single nonmincral 
such as coal, or an aggregate of several or more minerals 
such as granite, or a uniform substance such as volcanic 
glass, which could be considered a mineral if the chemical 
composition did not vary so irregularly from place to 
place. The most highly prized blue gem of ancient times, 
lapis lazuli, is a rock consisting of at least half a dozen 
individual minerals. Three gems obsidian, silica-glass, 
and tektite are natural glasses of volcanic origin, having 
wide ranges in their content of silica. 

Although it contains some mineral substance, pearl, 
"queen of gems/' is the product of a living organism. Coral 
consists of the skeleton of certain sea animals which be- 
long to the same group as the sea anemone. Jet is a plant 
material, a variety of coal, and so is not properly a mineral. 
Amber is surely a gem, and one of the loveliest, but it is the 
fossil resin of ancient trees. These four are organic gems. 

The synthetics and imitations, that is, the artificial gems, 
do not fit into any of these classifications. They may be 
regarded neither as minerals, nor rocks, nor organic things, 
but as chemical creations of the laboratory. Gemology is 
the only subject which properly considers them from every 

Characteristics of Gems 

A gem combines three significant qualities: chief among 
them is beauty ', so that it delights the eye; then durability, 
so that its beauty will last "unto the third and fourth gen- 
eration"; and rarity , so that one's neighbors may not < 
own any like it. Also, of course, a gem must be poi 
but, if it is used for personal wear, that can be tj' 

granted. Lacking any of these qualities, a material may 
not enter the exclusive ranks of gemology unless it pos- 
sesses the others to a high degree. 

Once a substance is admitted to be a gem, its current 
value is determined by a combination of economic, com- 
mercial, and political factors, such as adequate supply, 
fashion, publicity and demand, cost of cutting and mer- 
chandising, world prosperity and depression, international 
markets and tariffs. The final price of a very fine gem 
depends upon the conscience of the dealer and the acumen 
of the buyer. As the beauty-loving public becomes in- 
creasingly aware of the many previously little-known but 
valuable kinds of gems, the diff erentiation between precious 
and semiprecious stones becomes obsolete. If not com- 
mercially, at least aesthetically, they are equal. 

Gem Families 

As we glance over the rings in a jexvelcr's show case, 
we are amazed at the wide variety of gems he displays. 
But the gcmologist would recognize most of them as be- 
longing to a quite limited number of separate species, 
these in turn being represented by many varieties based 
mainly on differences of color. 

We may liken a gem species to a human family, for 
example, the Smiths, and compare a gem variety to any 
individual member of the family. Thus George Smith 
may be blond, whereas his brother Fred Smith may be 
dark; yet they belong to the same family. George, how- 
may look surprisingly like Henry Jones but not be 
d to him. Again, other men may be named Smith, 
' f*y belong to a different race tWy a*e not brothers 


of George and Fred. A scientific knowledge of gems en- 
ables us to trace any stone to its proper place on the 
gemological family tree. 

Gem Properties 

To be able to recognize gems requires both a familiarity 
with their appearance and a knowledge of their nature and 
characteristics. These qualities are called properties, as 
coldness is a property of ice, sweetness is a property of 
sugar, and heaviness is a property of lead. Each known 
property serves to identify a particular gem or to eliminate 
other gems as possibilities. At the beginning of the process 
of testing an unknown gem, all gems and their substitutes 
of similar appearance are under suspicion, but determining 
any definite property reduces immediately the long list of 
gems to a few likely ones. Knowing the properties of 
gems and being able to find them listed and described in 
convenient books and tables make gem identification a 
matter of systematic procedure. 

Some properties, such as color, are easily discerned, but 
others must be weighed and measured, sometimes with 
elaborate and expensive instruments. Many crystals, as 
well as a few other specimens, disclose their identity by 
means of the original forms in which they occur; other 
gems are most easily recognized by the properties that are 
revealed after cutting. 

Any gem species differs from all the rest in composition 
and structure. Its chemical elements, their kind and ar- 
rangement, give the gem its properties, and these in turn 
furnish us with the means of identifying the gem. 



Chemical tests are of little value in the recognition of 
gems; the information gained is hardly worth the damage 
done. Resistant as most gems are to normal wear, they 
still deserve to be handled with reasonable caution, and 
therefore a chemical examination is not made of cut gems, 
but only of rough stones or fragments. A few useful 
exceptions are described later. 

The chemical composition itself, nevertheless, is of great 
importance, if not in the actual identification of a gem, 
at least for an understanding of its constitution. Most 
gems are minerals, and the fundamental fact about a min- 
eral is that it is a naturally occurring chemical element or 
compound. The principal basis for classifying minerals, 
either scientifically or industrially, is a chemical one. 

The colors of gems are due mostly to the presence of 
chemicals, usually oxides of certain metals, which are often 
scattered through the stone as minute impurities in such 
small amounts that they are not included in the chemical 
formula. (There are only a few self-colored gems.) Such 
minor constituents make a gem less perfect but at the 
same time add to its beauty and so increase its price. They 
probably create more value than anything else in the world 
of the same weight. For example, each ounce of the 
chromium that gives emerald its green color adds perhaps 
a million dollars to the cost of the gem up to a certain 
limit, of course, for there is the law of diminishing returns, 
as well as a saturation point after which too much coloring 
matter may actually decrease the beauty of the gem. Evi- 
dence of the existence of these coloring substances is not 
revealed chemically, however, but optically, by means of 


the characteristic absorption spectra described later in this 

Diamond is the simplest in composition of all the gems, 
the only one consisting entirely of a single element, crystal- 
lized carbon. Tourmaline, at the opposite extreme, has 
such a complex formula that John Ruskin said, "The chem- 
istry of it is more like a medieval doctor's prescription than 
the making of a respectable mineral." Next to diamond 
in simplicity among the more important gems are the 
oxides, including quartz (an oxide of silicon) and corun- 
dum (an oxide of aluminum). 

More gems belong to the silicates than to the other 
chemical classes; included among them are feldspar, jade, 
tourmaline, beryl, olivine, garnet, zircon, and topaz. Tur- 
quoise is a phosphate. Spinel and chrysoberyl are 'Multiple 
oxides or aluvrinates. Pyrite is a siilfide. Fluorite is a 
halide, more accurately a fh/oride. Smithsonite is a car- 
bonate. Of the organic gems, pearl and coral arc also 
largely carbonates, whereas amber and jet are hydrocar- 
bons. Oxygen is the chief element present in gems, and 
silicon, aluminum, and calcium are next in abundance. 

The resistance of most gems to chemical action is im- 
portant from the standpoint of their durability. They 
may be properly expected to retain their pristine beauty 
almost forever. The enormously high temperature re- 
quired to cause even the slightest blackening of a gem 
diamond is an example of this stability. Glass imitations, 
on the contrary, become dull even if not worn, because 
of the deleterious effect of the hydrogen sulfide (which is 
also the cause of silver tarnish) present in the air. 

A few genuine gems are likewise n|tf inipervious to 
ordinary chemical action, and special caje^BtfWd be taken 


of them. Pearls, for instance, lose their luster if allowed 
tg remain long in contact with body perspiration. The 
popular belief that the beauty of pearls improves with 
wear seems hardly justified. The famous story of Cleo- 
patra dissolving two choice pearls in vinegar and drinking 
them to impress Antony with her wealth is probably not 
true, because the calcium carbonate is too much associated 
with organic matter to dissolve rapidly in such a weak 
acid as vinegar. But the moral is evident to wearers of 
gems, although it ought to be unnecessary to advise them 
to refrain from spilling acids on their jewels. All the 
varieties of garnet are somewhat susceptible to the effects 
of acid. Hydrochloric acid will attack certain gems, in- 
cluding turquoise, pearl, lapis la/Aili, and coral. Two 
strong acids are the ingredients of aqua regia, which is 
used for testing gold, and the jeweler should be careful 
where he places the gems when repairing or cleaning 
jewelry containing them. Grease may prove progressively 
injurious to gems that are to any degree porous, such as 
turquoise, moonstone, and pearl. Caustic alkalies injure 
emerald, and oil of turpentine removes the red coloring of 

Tests, of course, can be made of gems by means of any 
known property. For obvious reasons, as explained, a 
chemical examination is rarely made. But with appropri- 
ate care a few simple tests may on occasion be worth 

Ornaments and jewelry of "Mexican jade" virtually 
flooded the American market in 1943 and are still abundant. 
The identity of this material with the common mineral 
calcite is sfyown by the effervescence that occurs when a 
Irop of ! '.^cdMDc acid is placed on it. 


On turquoise advisedly on the under side if the speci- 
men has been cut a touch of hydrochloric acid leaves a 
dull spot which turns bright blue when a drop of am- 
monia is added, thus distinguishing the gem from its usual 

Coral and the other carbonate gems effervesce briskly 
in acid. Lapis lazuli in acid gives off the rotten-egg odor 
of hydrogen sulfide. Amber can be distinguished from 
other natural resins by its refusal to become sticky or dull 
when touched by a drop of ether. 

Just as a variety of a gem may, through gradual changes 
in the kind and amount of coloring matter, grade imper- 
ceptibly into a different variety as ruby wanes in depth 
until it becomes pink sapphire so also a mineral species by 
variation in its actual chemical formula may grade into 
a related species, which yet maintains (and indeed must 
have) the same type of crystalline structure. Thus, the 
six garnet species are more or less interchangeable in com- 
position among themselves. Other gem minerals, includ- 
ing corundum, spinel, olivine, and topaz grade into non- 
gem species. Both aspects of this relationship are known 
as isomorphism. 

Another and more complete type of chemical alteration 
entirely changes the composition and physical properties 
of a substance but preserves its characteristic outer form. 
The transformation is called pseudomorphism. Petrified 
wood is the most familiar example of a gem pseudomorph, 
the chalcedony variety of quartz having replaced the 
original substance, wood. As the trees decayed, tiny par- 
ticles of silica that had infiltrated among the original ce r 
settled out of solution and slowly replaced the fibe* 


A different condition, called polymorphism, exists when 
the same chemical element or compound produces different 
minerals. Thus, diamond and graphite are both composed 
solely of carbon; and three gems kyanite, andalusite, and 
si llimanite share a single formula. 


Abbe Haiiy called crystals "the flowers of the mineral 
kingdom." It is easy to agree with him, upon examining 
the beautiful crystals of gems with their symmetrical forms 
and shining faces. The shape in which we find them is the 
shape that they have always had, for like people and ani- 
mals, the larger crystals are merely small ones "grown up." 
Growth is usually a long, slow process, taking perhaps 
thousands or even millions of years, although sometimes it 
may be rapid enough to be seen happening. Crystals vary 
in size from those that are colloidal and are visible only 
with an ultramicroscope to those that weigh a number of 
tons. Unlike living organisms, crystals grow by accumu- 
lation from the outside rather than by expansion from 
within. When growth is interrupted for some reason and 
then begins again, a "phantom" crystal may appear en- 
closed within the larger one. 

Crystal structure is a fundamental property of minerals 
and crystal shape provides a valuable clue to the identity 
of a rough specimen. Crystallography is largely mathe- 
matical in treatment, and in part it is very complicated. 
An elementary knowledge of crystals, however, is worth 

ving, if only for the ability that it gives to name many 
in their native state without testing them further. 

The regular external shape of a mineral is the outward 
evidence of its internal atomic structure. If a crystal is 
broken or cut for jewelry, each piece, no matter what its 
size or outline, will still have the same internal pattern, as 
shown by X-ray studies. All gem minerals, with the pos- 
sible exception of opal, are crystalline substances, as are 
also those artificial gems that are correctly called syn- 
thetics. The minute particles, the atoms and ions, of 
which they are composed, are arranged throughout in a 
definite, orderly manner and are held together in a "lat- 
tice" by electrical attraction, usually that of oppositely 
charged electrified units called ions. Amorphous or non- 
crystallive substances were created under conditions un- 
favorable to a systematic arrangement of their atoms, 
which are arranged instead mostly at random. The dif- 
ference is somewhat like that between soldiers at inspec- 
tion and a group of children watching a fire. Amorphous 
gems may be fashioned into any neat design, but their 
internal structure is still irregular and they can never be 
crystalline. That is why the term "rock crystal" for 
even the finest of etched glassware is wrong; only natural 
unfused quartz should be thus designated. 

The "habit" of a gem crystal is the form or combina- 
tion of faces typical of it. Sketches and models show an 
ideal shape, but in nature crystals are never perfect, some 
bdng malformed, others broken just as every tree is bent 
a little, every flower is a bit distorted, and every person 
has some blemish which distinguishes him or her fro 1 " 
the figures in the tooth-paste advertisements. Ne^ - 
less, the angles between the natural faces are alwa) 
stant and are more accurate than human skill could 
them. In addition to individuals, crystals occur as t 


three of which are illustrated in Figs. 2-4, and in groups. 
The large number of crystal forms may be separated 
into six main divisions called systems, according to the 
arrangement of axes within the stone. (See Figs. 5-10.) 
These axes are entirely imaginary, however, like the poles 
of the earth or the lines of latitude and longitude on a 

Fig. 2 Fig. 3 Zircon Fig. 4 Staurolite 


Models of Typical Twin Gem Crystals 

The letters are conventional symbols for the common "forms." [From 
Hurlbut Dana's Manual of Mineralogy, copyright 1941.] 

map, and like them are extremely useful. The six systems 
are called isometric, tetragonal, hexagonal, orthorhombic, 
monoclinic, and triclinic. Each of them has three axes 
except the hexagonal, which has four. The axes in the 
isometric system are of equal length. The six systems may 
further be subdivided into a total of 32 crystal classes or 
230 space-groups, according to symmetry. Practically all 
?ems, as well as most minerals, are confined to a relatively 
.: these categories. 

classification of crystals is not in the least arbitrary 

..ificial, in spite of the imaginary conception of an 

The atomic arrangement of minerals determines 


most of their properties. Since the internal structure de- 
termines the crystal forms also, it follows that certain 
properties, the optical properties in particular, must be 

Fig. 5 Isometric 

Fig. 6 

Fig. 7 

Fig. 8 Orthorhombic Fig. 9 Alonoclinic 

Fig. 10 

The Six Crystal Systems 

Each model shows how different "forms" may have the same crystal 
axe's. Many other combinations are possible in each system. [From 
Dana-Ford A Textbook of Mineralogy, copyright 1932.] 

related to the crystallization. The identification of a gem 
is largely dependent upon a knowledge of the cry 
system to which it belongs. Let us take the systems r 
by one and mention some of their characteristics; later 


shall learn how such theoretical considerations of gemology 
are intimately related to the practical testing of gems. 

To gain a better understanding of what crystals are, 
shake out a few grains of common table salt and look at 
them with a magnifying glass pretty little cubes they are! 
Now it is easy to understand why this system is called 
the isometric, meaning equal measure: all sides are equal and 

Fig. 11 Spinel Fig. 12 Garnet Fig. 13 Pyrite 

Typical Isometric Gem Crystals 
[From Hurlbut Dana's Manual of Mineralogy, copyright 1941.1 

the angles between them are equal. These facts are true 
of all simple members of this system, whether or not the 
crystals form a cube. Diamond, for instance, usually oc- 
curs in octahedrons resembling two square pyramids placed 
base to base, but the sides and angles do not vary from 
the requirement. Other isometric gems are spinel (Figs. 
11 and 7L), garnet (Figs. 12 and 78), fluorite (Fig. 72), 
sphalerite, and pyrite (Figs. 13 and 81). 

The tetragonal system is usually represented by prisms 
* r \ pyramids. The most important gem representative is 
con (Figs. 14 and 79); cassiterite (Fig. 15), scapolite, 
1 idocrase (Fig. 16) are also tetragonal. 


Some of the finest crystals belong to the hexagonal 
system. It is not generally realized that snow and ice 


Fig. 15 


Fig. 16 

Typical Tetragonal Gem Crystals 
[From Hurlbut Dana's Manual of Mineralogy, copyright 1941.] 

are minerals, but photographs of snow crystals taken under 
a microscope show their wonderful six-sided structure. 







i m 

a 777 < 

Fig. 17 

Fig. 18 


Fig. 19 

Typical Hexagonal Gem Crystals 
[From Hurlbut Dana's Manual of Mineralogy, copyright 1941 

Corundum (ruby and sapphire, Figs. 17 arur* r 
(emerald and aquamarine, Fig. 18), tou m; 

75, and 76), and quartz (amethyst, rock crystal, etc., Fig. 
93) are the best-known members of this system. Quartz 
crystals occur, both alone and as large clusters, in familiar 
prisms which are pointed at the ends and are the most 
easily recognized of all the minerals. Beryl, because of its 
flat terminations, is also quickly identified. Tourmaline is 

Fig. 20 Fig. 21 Fig. 22 

Topaz Olivine Chrysobcryl 

Typical Orthorhombic Gem Crystals 
[From Dana-Ford A Textbook of Mineralogy, copyright 1932.1 

the only mineral that shows a triangular outline when 
viewed down the length of the crystal. Additional hex- 
agonal gem crystals include apatite, benitoite (Fig. 74), 
phenakite, willemite, and hematite. 

Gems that belong to the orthorbowbic system are often 
complex in their crystal forms. The most important ones 
are topaz (Figs. 20 and 80), oiivine (Fig. 21), and chryso- 
beryl (alexandrite and cat's-eye, Fig. 22); lesser ones in- 
clude cordierite, danburite, andalusite, sillimanite, and stau- 
rolite (Figs. 90-92). 

(i< n crystals of the inonodmic system include spodu- 
*'* hite and kunzite, Fig. 73), orthoclase feldspar 
gv 23), and sphene (Fig. 24), as well as 
i 21 

bra/ilianite, diopside, epidote, datolite, euclase, and gypsum 
(satin spar, Fig. 25). 

Fig. 23 



Fig. 24 

Fig. 25 

Typical Monoclinic Gem Crystals 
[From Hurlbut Dana j s Manual of Mineralogy, copyright 1941.1 

The triclimc system is represented by microcline feld- 
spar (amazonstone, Fig. 85) and plagioclase feldspar (lab- 

Fig. 26 Fig. 27 Fig. 28 

Plagioclase Axinite Rhodonite 


Typical Triclinic Gem Crystals 
[From Hurlbut Dana's Manual of Mineralogy, copyright 1941.] 

radorite, Fig. 26), axinite (Fig. 27), kyanite, and rhodonite 
(Fig. 28), and by the only turquoise which has ever been 
found in crystals. 


Some gems act as if they were ashamed of themselves 
and attempt to conceal their identity by assuming the forms 
of quite different substances. In addition to this type of 
replacement, described in the previous section as pseudo- 
morphisin, gems occur also in imitative shapes, for example, 

Fig. 29 Dendrites on Marble 

when chalcedony resembles a bunch of grapes, and when 
agate or marble shows manganese or iron markings that 
look like trees and moss (see Figs. 29 and 95). Gems 
whose irregular outer shapes do not warrant distinctive 
names are referred to as massive. 

In spite of the fact that most of the properties of gems 
are directly determined by their internal structure, no one 
has ever seen an atom. Because they are so small, millions 
of them can occupy an inch of space. But their presence 
and even their position are subject to proof. In 1912 von 


Laue passed X-rays through a crystal and onto a photo- 
graphic plate. The many symmetrical spots that appeared 
on the plate (see Fig. 30) were found to be visible evidence 
of the atoms in their specific arrangement. Further re- 

Fig. 30 X-ray Picture of Beryl (Fmerald and Aquamarine) 

[From St. John and Isenburger Industrial Radiology , 2nd edition, 
copyright 1943.] 

search has opened the door to a vast field of knowledge 
regarding the structure of crystals those marvelous ex- 
amples of Nature's architecture. 


It is the effect of light upon a substance which deter- 
mines whether it is beautiful, and beauty is the pnme 


attribute of every gem. Optics, the science of light, is 
therefore the most important part of gcmology. In or- 
dinary technical usage it is generally considered a branch 
of physics, and the properties of minerals are hence divided 
into those that are physical, including optical, and those 
that are chemical. The great significance of optics in the 
study of gems, however, as contrasted with the small prac- 
tical value of chemical tests, such as have already been 
discussed, justifies a further separation here into optical 
properties and physical properties. 


Through the doorway of color we enter the enchanted 
world of gems. In former times gems were recognized 
mainly by their colors, green stones being called emerald 
and red stones ruby, so that the superstitions which gath- 
ered about a gem applied to all of a similar color. The 
wealth of curious gem lore is concerned mostly with the 
symbolism of color. The intense emotional effect of color 
language appears through all literature. 

It seems probable that the explanation of the fact that 
women are more responsive than men to the lure of gems 
is the physiological one that they have a superior sensitivity 
to color stimuli. Men are often at least partially color 
blind, but women are rarely so and generally have a more 
acute judgment of color. 

Without beauty of a degree high enough to please almost 
everyone, no substance, however rare or durable, can 
secure entrance to the select circles of gem society. 
Usually color is the main factor of beauty, and in some 
instances it is the only factor, as in stones that are not 


transparent or brilliant, such as coral, jade, lapis lazuli, 
turquoise, the chalcedonies, and especially opal. Because 
the permanent beauty of gem colors is, therefore, the chief 
single reason for the firm hold that precious stones have 
always had upon the affections and the imagination of 
mankind, the study of color in gems is one of the gemolo- 
gist's most important tasks. It is approached from the 
scientific as well as the aesthetic viewpoint. 

Color is, in a sense, all that we see of light. It is mostly 
a difference in color, no matter how little, that makes an 
object visible against its surroundings. White light con- 
sists of separate rays or wavelengths, successively red, 
orange, yellow, green, blue, indigo, and violet, all perfectly 
blended and reaching the eye simultaneously. By means 
of a simple glass prism, such as Newton is said to have 
bought at Stourbridge Fair for a penny, his classic experi- 
ment may be repeated, and a beam of sunlight may be 
split up into its sequence of rainbow colors, called the 
spectrwn (see Fig. 41). 

When white light is reflected from the surface of a 
stone or passes through it, some of the component wave- 
lengths are absorbed, while the rest unite to produce the 
color of the gem. (The process of absorption causes a 
transfer of energy from light into heat, which means into 
the motion of the atoms of the gem itself.) Slight but 
uniform absorption results in a colorless stone, whereas 
complete absorption makes it black. The precise hue of 
the gem depends upon the extent to which the parts of the 
spectrum are eventually transmitted to the eye. Anyone 
listening to orchestral music can easily distinguish the 
high notes of the violins from the low notes of the horns. 
But unlike the ear, the eye fails to make such a sep; v -, ' 

Fig. 31 Jeweler's Loupe Fig. 32 Utility Magnifier 

Fig. 33 Hand Lenses 

Magnifying Instruments for Examining Gems 

[Bausch and Lonib; American Optical Co. 

and can see only a blending of colors. Red light and 
green combine as yellow; blue and yellow, being com- 
plementary, are seen as white. Actually the color of most 
gems is such a harmony of hues. Amethyst appears violet 
because it returns only those rays whose combined fre- 
quencythat is, number of vibrations per second gives 
the effect of this particular color. The same rule applies 
to opaque gems. 

Yet the vast mystery of color remains largely unsolved. 
One may even say that we do not know anything about 
what causes color what makes one flower yellow and 
another violet; why one form of chromium colors emerald 
an exquisite green, and a different form of the same element 
gives a glorious crimson to ruby. So too it may be said 
that we do not know what electricity is, but we harness 
its power and press it into our service. Since Newton 
observed his first spectrum, color technology has con- 
stantly progressed, and chemists have devised artificial 
sources of coloring materials which have helped to brighten 
the lives of us all. 

Gemology shows how often appearances are deceptive. 
Many of the stones which look alike have no similarity 
other than their color; some which seem to have no re- 
semblance whatsoever are really "sisters under their 
skins." Mere traces of foreign matter, accidentally in- 
troduced, may give a wide range of hues. Those stones 
whose color is caused by chemicals that are an inherent 
part of them are called idiocbrotnatic', if the color is elim- 
inated, the identity of the stone is destroyed. Most gems, 
however, are allochrowatic; the color is an incidental char- 
acteristic; if it were altered or removed the essential prop- 
erties of the stone would remain as they were before. It 


is not easy to visualize the sameness of two gems that look 
as unlike as a red ruby and a blue sapphire both varieties 
of the same mineral, corundum, differing only in color. 

Thus color, though surely the most important quality in 
a gem, may be the least reliable guide to its identification. 
But the delicate color sense possessed by many persons can 
distinguish the subtle yet vital differences in hue that char- 
acterize most individual gems and are peculiar to them. 
Even without this precise ability, knowing the approximate 
color narrows the choice of gems to relatively few. In 
spite of all sensible advice to the contrary, therefore, most 
persons will continue to rely on their instinctive judgment 
of color to make a preliminary guess as to the name of a 

Printed descriptions of gem colors are of little use for 
this purpose, and practical experience in the actual handling 
of gems is necessary. When this way is no longer effec- 
tive, because of the difficulty of discriminating between 
several gems of the same color, aid is sought from one 
of the instruments (described later) that analyzes color, 
such as a spectroscope (Fig. 47) or dichroscope (Fig. 48). 


Some gems, like many humans, show their true color 
when put to a test. The test of a gem is to determine its 
color when it is finely divided. By rubbing the stone on 
a piece of unglazed porcelain, such as a rough white tile, 
a powdered streak is made, which may have a color very 
different from that of the solid specimen. 

Many minerals have a characteristic streak, but only a 
few gems show the property in any color except white. 


Of these gems, hematite is the most important. As a 
metallic dark-gray gem it has been worn for years in a 
larger number of men's signet rings (carved with intaglio 
portraits) than all other gems combined. By its rich 
reddish-brown streak it can be distinguished from any other 
gray or black mineral or substitute. Pyrite, another iron 
mineral, appears to have a metallic yellow color resembling 
brass, but its streak is almost black with a greenish or 
brownish cast. 

Reflection and Luster 

When light strikes a gemstone, some of it is reflected 
immediately from the surface, some of it is absorbed at 

the surface, and the rest 
passes through. (See Fig. 
34.) The amount that is 
reflected varies according to 
the direction of the light 
and the nature of the gem. 
Only a small part of the 
light falling perpendicularly 
is turned back to the eye, 

Fig. 34 Reflection and Re- 
fraction of Light in a Gem 

but most of the light is re- 
flected when the angle is 
small. The greater the re- 
flection, the brighter the stone will appear. 

This appearance of the surface of a gem in reflected 
light is called luster. Hard stones which have a more 
closely knit surface structure can generally be given a 
higher degree of polish than others; in consequence they 
will allow less light to penetrate and more will be re- 


fleeted. A rough surface scatters the light and gives a 
diffused luster, as in stones that are soft (such as tur- 
quoise) or have a granular texture (such as certain jade). 
The common, though hardly sanitary, habit that mineral 
collectors have of wetting with their tongues a newly 
found agate to bring out its color serves the purpose (be- 
sides cleaning it) of providing a thin but level surface of 
moisture to reflect the light regularly, similar to the result 
obtained with much more difficulty by polishing the 
stone. While being polished, the surface of every gem 
except diamond is momentarily caused to flow, the liquid 
spreading evenly over the stone in an extremely fine layer. 
Gems with a high refractive (light-bending) power 
produce the most brilliant luster. Adamantine luster, as 
indicated by its name, is typical of diamond. Most gems 
have a vitreous luster, which is simply the surface appear- 
ance of ordinary glass. Subadawantine luster applies to a 
number of intermediate gems, including zircon, sphene, 
and andradite garnet, the lusters of which exceed that of 
glass but do not quite attain the splendent beauty of 
diamond. Resinous luster indicates the surface of a resin, 
of which amber is the only gem representative. An oily 
surface has a greasy luster. Fibrous gems such as satin 
spar show a silky luster. Turquoise has a waxy luster. 
The luster of pearl is obviously pearly, as is also that of 
most crystal cleavage faces. The opaque metallic gems, 
pyrite and hematite, possess a metallic luster. Most of 
these terms are descriptive enough to be evident after a 
brief examination of a gem that is characteristic of each. 
Considered especially with its color, the luster of a gem is 
frequently a useful guide to the quick recognition of its 
spec '"" 



The light that is not reflected or absorbed at the surface 
of a gem enters the interior, where its subsequent action 
has- a profound effect upon the beauty of the gem and 
is of great value in revealing the identification. The speed 
of light in air is well known to be about 186,300 miles a 
second. When it enters a gem, however, light is slowed 
down, and this change in velocity deflects its direction, 
except where it happens to strike exactly perpendicularly. 
We say that the light has undergone refraction or bend- 
ing, as shown in Fig. 34. Every South Seas native is 
familiar with this property of light when he spears a fish 
in water by aiming, not where the fish appears to be, but 
where he is sure that it really is. The apparent bending 
of a stick in water is similar evidence of the refraction of 
light. The slower the velocity of light in a given gem, the 
greater is the amount of refraction, as if a slow ray were 
less determined than a fast one and had more difficulty in 
keeping to its path. In any event, the light that comes 
in at an angle is bent nearer to a vertical direction. 

The actual amount of deviation is determined mathe- 
matically and is expressed as a number called the refrac- 
tive index for diamond it is 2.42, that is, light goes almost 
two and one-half times as fast in air as it does in the stone. 
Gems that have a high refractive index are said to be 
optically dense; in them the light is bent sharply and its 
velocity is relatively slow. Light that comes out of a gem, 
as of course it must to become visible, is also refracted 
but in the opposite direction (that is, away from the ver- 
tical) because it is then entering a substance (air) that is 
optically less dense than the stone. 


As the angle of inclination of the light within the gem 
increases, the light finally reaches a critical angle (Fig. 35) 
when it can no longer be refracted out of the stone and 
unable to escape is totally reflected so that it stays inside. 

When total internal reflection takes place at the bottom 
of a gem, as shown in Fig. 35, leakage of light is prevented 
and the light, instead of passing out through the lower 
facets, is returned to the 
top and refracted out from 
there, adding to the bril- 
liancy of the stone. Light 
traveling inside a gem emer- 
ges from the stone when it 
strikes a facet surface at less 
than the critical angle. Con- 
versely, when it strikes at 
greater than the critical 
angle, it is totally reflected, 
without loss, within the gem. 
The critical angle of a gem is inversely proportional to the 
refractive index. Diamond, for example, having a higher 
index (2.42) than white topaz (1.61), has a smaller critical 
angle. (See Figs. 36 and 37.) Less light is lost, therefore, 
and more can be totally reflected internally in a diamond 
than ih any of the gems that have a smaller refractive index. 
Skillful cutting enables light to traverse a diamond so as 
to be returned finally to the eye with as little loss in quan- 
tity and as much improvement in quality as possible. Thus 
the fiery brilliancy, is produced that is diamond's chief 

A number of methods are available for determining the 
refractive index. For a cut stone the most convenient is 


Fig. 35 Total Internal Re- 
flection in a Gem 

by means of a refractometer made especially for gem test- 
ing (Fig. 38). This instrument gives a direct reading on 
a simple scale. The gem is placed with one of its facets 

Fig. 36 Diamond Fig. 37 Topaz 

Critical Angle in Two Gems 

against the refractometer lens, which is a prism or hemi- 
sphere made of glass with a high refractive index; a drop 
of some highly refractive oil is put between them to ex- 

Fig. 38 Section Through a Refractometer 

elude the air and bring them into optical contact. Light 
from an outside source, either natural or artificial, is di- 
rected through the refractometer lens and against he flat 
bottom surface of the stone. The portion of the light nu 


strikes at more than the critical angle is totally reflected, 
as already described, and produces a band of light, the edge 
of which is read on a graduated scale (Fig. 39) and cor- 
responds to the refractive index of the gem. 


Fig. 39 Singly 
Refractive Gem 


Fig. 40 Doubly 
Refractive Gem 

Refractometer Scale 

' The range of standard refractometers is not high enough 
to include four important gems diamond, zircon, sphene, 
and andradite garnet whose brilliancy is too great and 
whose critical angle is therefore too small to register, unless 
a special lens of higher refractive index is used. The very 
absence of a reading points immediately to one of these 
four species. 

No i lore fundamental or easily determined property of 
"f-i^ is av-ii'ible for purposes of identification. Typical 


values, selected from G. F. Herbert Smith's Gewstones. 
are listed here. Two sets of figures are given for doubly 
refractive gems. (See page 39 and Fig. 40.) 

Refractive Index Table 

Diamond 2.42 

Sphalerite 2.37 

Cassiterite 2.00 2.09 

Sphene 1.88-1.92 1.99-2.05 

High zircon 1.92-1.93 1.98-1.99 

Andradite garnet 1.89 

Low zircon 1.79-1.84 

Spessartite garnet 1.79-1.81 

Almandite garnet 1.75-1.81 

Corundum 1.76-1.77 1.77-1.78 

Chrysoberyl 1.74-1.75 1.75-1.76 

Pyrope garnet 1.74-1.75 

Grossularite garnet 1.74-1.75 

Spinel 1.72-1.75 

Olivine 1.64-1.67 1.68-1.71 

Spodumene 1.65-1.67 1.67-1.68 

Jadeite jade 1.65 1.67 

Topaz 1.61-1.63 1.62-1.64 

Tourmaline 1.62-1.63 1.63-1.64 

Turquoise 1.61 1.65 

Nephrite jade 1.60-1.61 1.63-1.64 

Beryl 1.56-1.59 1.56-1.60 

Quartz 1.54 1.55 

Amber 1.54 

Orthoclase feldspar 1.52-1.53 1.53-1.54 

Opal 1.44-1.46 

Fluorite 1.43 



The separation of white light into its component colors, 
accomplished by Newton with his penny prism, proves 
not only that light is bent upon entering a substance of 
different refractive index, but also that each color of the 
spectrum is refracted to a different extent, as shown in 

Fig. 41 Dispersion of Light in a Gem 
The amount of fire is exaggerated. 

Fig. 41. This spread of colors is called dispersion; in a 
gem it is known as fire. 

A superior example of dispersion is the rainbow; sunlight 
is refracted and dispersed by countless millions of rain- 
drops which together magnify this simple effect into the 
wonder of a stormy sky. A myriad of tiny rainbows spar- 
kling in the morning dew, or on a crack in a window, or 
from the depths of a diamond these are other familiar 
dispersion effects. 

Red light rays are bent the least, and violet rays at the 
other extreme are bent the most. Since red rays are bent 


less than the rest of the colors, their velocity is changed 
less than that of the others, and their refractive index is 
slightly lower. Actually, the refractive index of a gem 
is different for each color, and the difference between 
the 'end values of red and violet measures the dispersion. 
The indices of refraction of diamond, for example, range 
from 2.41 to 2.45, and therefore the dispersion is 0.04. The 
wider the spread, the greater is the fire. 

Fire is therefore not mere brilliancy, which is internal 
reflection of white light, although, in general, highly re- 
fractive gems also possess the most dispersion. In colored 
stones the hues of dispersion are masked by the color of 
the material itself. Contrary to what might be supposed, 
diamond does not have more fire than any other gem. Both 
andradite garnet and sphene, as well as cassiterite and sphal- 
erite, surpass it in dispersive power and would appear even 
more spectacular than diamond if they too were colorless. 

Typical values of selected gems are given below. 

Dispersion Table 

Sphalerite 0.16 

Cassiterite 0.07 

Andradite garnet 0.06 

Sphene 0.05 

Diamond, benitoite, zircon 0.04 

Epidote, grossularite garnet, spes- 

sartite garnet, pyrope garnet 0.03 
Almandite garnet, spinel, olivine, 
corundum, spodumene, tour- 
maline, chrysoberyl 0.02 
Topaz, beryl, quartz, orthoclase 
feldspar, fluorite 


Double Refraction and Birefringence 

The behavior of light as thus far described is strictly 
true only for gems that are amorphous or belong to the 
isometric system of crystallization. Gems that belong to 
the other five crystal systems have a somewhat different 
effect upon a ray of light. These gems split a single ray 

Fig. 42 Double Refraction Fig. 43 Double Refrac- 
in a Gem tion in Calcite 

into two new rays, each of which travels with a different 
velocity inside the stone and is bent a different amount. 
(See Fig. 42.) The slower of the two rays is refracted 
more than the other, and each ray has a separate refractive 
index, as if the gem had a dual personality. 
' This double refraction is possessed to such an extreme 
degree by the common mineral calcite that any mark, such 
as a line or dot or row of print, shows double when seen 
through it (Fig. 43). Although the effect is observed to 
a much less extent in the gemstones, some gems display it 
under a magnifying glass, jeweler's loupe, or microscope. 
A doubling of the edges of the back facets appears when 
the- -e viewed through the front of the stone; two lines 
>ach line that actually joins a pair of facets. 

Such an experiment should be attempted only in a state of 
complete sobriety. The double refraction of zircon and 
olivine, as well as of benitoite and cassiterite, is so strong 
that a reading glass is sufficient to show it, and the doubling 
in sphene can be seen with the naked eye. 

A simple test for double refraction, which is perhaps the 
most satisfactory way to distinguish zircon from diamond, 
requires only sunshine and a card with a small hole pierced 
in it. Holding the card between the sun and the stone 
permits the narrow beam of sunlight that comes through 
the opening to be doubly refracted by the gem and thrown 
back onto the card as a group of double spots; it is proved 
that the gem does not belong to the isometric system and 
cannot be a diamond. 

One precaution is necessary. Gems of the tetragonal 
and hexagonal systems are imiaxial (Fig. 44), having one 
direction in which the light is not doubly refracted; this 
direction is called the optic axis and must be avoided in 
making the examination, because it will cause the gem to 
seem to be amorphous or isometric. Gems of the three 
remaining crystal systems orthorhombic, monoclinic, tri- 
clinic are biaxial (Fig. 45), having two such directions of 
single refraction and thus having two optic axes. A gem 
should, therefore, be inspected in more than two directions 
before an opinion is expressed. 

' One of the two rays that form when light enters uniaxial 
crystals (tetragonal and hexagonal) it may be either the 
slower or faster ray, depending upon the gem varies in 
speed according to the direction in which it happens to 
vibrate, and consequently has a variable refractive index, 
which reaches a certain limit. Biaxial crystals (orthorhom- 
bic, monoclinic, and triclinic) also have two ravs - r elin w 


through them in any given direction, but these gems are 
much more complex in their optical nature and possess 
three principal refractive indices. 

The amount or strength of double refraction is called 
birefringence and is measured by the difference between 
the largest and smallest indices, whether there are two or 

Optic axis 

Optic axes 

Fig. 44 Uniax- 
ial Gem 

Fig. 45 Biaxial Gem 
Possible Arrangement of Optic Axes in Gems 

three. For example, quartz has two refractive indices of 
1.54 and 1.55; the birefringence is the difference, 0.01. 
Amorphous and isometric gems, being singly refractive, 
obviously have no birefringence. 

' When a doubly refractive gem is tested on the refrac- 
tometer, the band of light ends in two parallel lines. These 
may move somewhat on the scale as the stone is turned, 
but their extreme high and low readings correspond to the 
maximum and the minimum values of refractive index. 
The most strongly birefringent gems show, of course, the 
widest separation of the terminal lines. 

Typical values of selected transparent gems are given 
the following page. 


Birefringence Table 

Sphene 0.12 

Cassiterite 0.10 

High zircon 0.06 

Benitoite 0.05 

Datolite, olivinc, epidote 0.04 

Diopside 0.03 

Tourmaline, spodumene 0.02 
Chrysoberyl, quartz, corundum, 

topaz, orthoclase feldspar, beryl 0.01 

Absorption Spectra 

Light that has undergone dispersion can be analyzed by 
one of the most amazing tools of modern science, the spec- 
troscope. This incredible instrument reveals the particu- 
lar combination of rays absorbed from the original white 
light during its passage through a gem. Each ray is a 
definite part of the spectrum, and those rays that are not 
absorbed unite to give the color of the gem. A full normal 
spectrum is seen in a direct- vision spectroscope (Fig. 47) 
when it is pointed merely at a source of light, but, when a 
gem is held between them, dark vertical lines or ribbons 
appear, obscuring certain sections of the spectrum. These 
absorption bands represent the rays that have been removed 
by the chemicals present as impurities in the gem. Each 
element produces a characteristic arrangement of bands, 
which together constitute an absorption spectrum. Two 
gems of apparently the same color may absorb light dif- 
ferently because they are composed of entirely different 
chemical combinations. Many a gem has its own i 1 ' 
tinctive absorption spectrum, which, in addition to furr' 


ing valuable knowledge about the cause of color in the 
gecii, is also useful in its identification. 

'Fig. 46 Petrographic Microscope Fig. 47 Direct- Vision 


Optical Instruments for Identifying Gems 

[Bausch and Lomb.l 

For several important gems the absorption spectrum is 

particularly useful. Zircon shows through the spectro- 

- c a multitude of sharp bands that conclusively label 

specimen. Ruby is rather fickle; its band may be 


either dark or light, depending upon the source of light, 
but it is always in the same place. The bands for emerald 
serve to differentiate it from all substitutes. Almandite 
garnqt was, with zircon, the first gem to be observed with 
a spectroscope and still is one of the best to be tested in 
this way. The mystifying change of color seen in alex- 
andrite--'^ emerald by day, an amethyst by night" is 
explained by its absorption spectrum, which shows a chro- 
mium compound having delicately different powers of 
absorption that vary according to the kind of illumina- 


We have already remarked that the color of a gem is in 
reality a combination of all the hues that are not removed 
from the original white light in its passage through the gem. 
Each of the two rays produced by doubly refractive gems 
not only is refracted differently from the other and ac- 
quires a different velocity, but also is usually absorbed to 
a different extent and has a different color. This twin- 
color effect is known as dichroism, as the word itself 

The complex biaxial gems (those belonging to the ortho- 
rhombic, monoclinic, and triclinic systems) possess three 
main color directions, corresponding to the three principal 
refractive indices, but only two colors can be observed at 
a time. 

A few strongly dichroic gems, especially kunzite and 
tourmaline, may show a change in color as they are turned 
in various directions. Even weakly dichroic gems are en- 
hanced in beauty by the subtle gleams of color glowim 


and mingling mysteriously in their depths. To reveal the 
twin colors of most gems with certainty, however, an in- 
expensive instrument called a dichroscope (Fig. 48) is 
required. It consists of a short tube having a round open- 
ing at one end and a square opening at the opposite end. 
Between the ends is fitted a piece of the clear variety of 
calcite known as Iceland spar; a magnifying lens may be 
added to enlarge the image. Through the round hole the 

Fig. 48 Section Through a Dichroscope 

observer looks at a gem held beyond the square opening. 
The great doubly refractive power of calcite (Fig. 43) 
makes this square appear as if it were two squares side by 
side and intensifies the original double refraction of the 
gem. Each of the two rays emerging from the gem is 
seen in a separate frame. Viewing the twin colors next 
to each other thus simplifies the comparison. 

The colors should change places slowly as the dichro- 
scope is rotated, and any difference between them, no 
matter how slight, is evidence that the gem is doubly re- 
fractive and therefore cannot be amorphous or belong to 
the isometric crystal system. The reverse is not true, how- 
ever, because not all doubly refractive gems show dichro- 
ism. A few, particularly zircons of colors other than blue, 
are so feebly dichroic that a good imagination is required 
to see the effect. Obviously, also, since this is a test involv- 


ing color, no colorless gem can be dichroic. Trying to 
find dichroism in a colorless stone would be like looking 
for a white rabbit hiding in a snowdrift. In addition, 
examination must be made in more than two directions 
through a gem, because there is no double refraction and 
consequently no dichroism along an optic axis (Figs. 44 
and 45). 

This "magic eye" is of the utmost value in gemology, 
separating many stones whose blending of colors gives 
them the same superficial appearance. In 1907 some blue 
stones that looked like sapphires were discovered to be a 
new kind of gem, and even an entirely new mineral, now 
called benitoite, because a California jeweler chanced to 
hold them in front of a dichroscope, which showed him 
a blue square and a white one, a combination never seen in 

Among the more important gems, ruby may be unfail- 
ingly identified by its distinct twin colors, yellowish red 
and purplish red, whereas red spinel and garnet (being 
isometric) and red glass (being amorphous) show no di- 
chroism at all. Similarly, blue sapphire can be told imme- 
diately from blue spinel or glass, and emerald can be 
distinguished easily from demantoid, the green garnet. 
Precise dichroic effects are difficult to describe, and they 
vary considerably with the hue of the gem itself, so that 
a table of dichroism would be useful merely as a hint. 
The appearance of the colors themselves becomes familiar 
only with experience. It must be remembered that, ex- 
cept for stray interference from outside light, even the 
faintest difference between the two colors proves dichro- 
ism and double refraction. 



Polarized light has become a household commodity in 
America chiefly through the widespread use of sun glasses 
made from Polaroid Film. This artificial material, com- 
posed of synthetic organic crystals embedded in parallel 
orientation in a plastic sheet, produces cheaply and con- 
veniently the same effects of polarization that occur in 
minerals. The features of polarized light that pertain to 
gems have already been discussed under different headings, 







Fig. 49 Light Polarized by a Gem Crystal 

but popular interest in this fascinating subject makes it 
worth while to mention briefly the relationship between 
polarization and some of the other properties of gems. 

Ordinary light vibrates in every direction at right angles 
to the path in which it is traveling forward, as shown at 
the left of Fig. 49. These vibration directions may be 
likened to the spokes of a wagon wheel, although there is 
no limit to their number; the axle corresponds to the ad- 
vancing path of the light ray itself. Polarized light, on 
the other hand, vibrates in only one direction, comparable 
to a single spoke on each of the opposite sides of the hub, 
making a straight line at right angles to the moving ray of 
light. (See Fig. 49.) 

Part of ordinary light becomes polarized when it is re- 
flected from the polished surface of a gem, the amount 


depending upon the angle at which it strikes. Part of the 
light that enters a singly refractive gem one that is amor- 
phous or isometric is also polarized. All the light that 
enters, a doubly refractive gem, however, is completely 
polarized, except along an optic axis; each of the two rays 
created by double refraction vibrates almost perpendicu- 
larly to the other. 

It is this individual restriction of the vibration directions 
that makes each ray of a doubly refractive gem so dis- 
tinct in its action and so useful in the identification of gems. 
When either of the rays is extinguished or obscured, the 
other predominates. A plate cut from tourmaline absorbs 
one of the polarized rays and permits only the other to 
pass through. If two such plates are "crossed," that is, 
held together, one lengthwise and the other sideways, as 
shown in Fig. 49, the first plate will pass the light that 
vibrates in its own lengthwise direction, but the second 
plate, being set in opposition, will stop the light. This 
striking phenomenon is shown in Fig. SO. A complete 
rotation of either plate brings alternating darkness and 
light four times. A doubly refractive gem rotated 
between the plates also causes this "extinction" (as the 
positions of darkness are called) to take place. Singly 
refractive gems present a dark field in all positions. 

A lone plate of tourmaline rotated behind a dichroic 
gem makes the twin colors alternate. Except that it does 
not absorb one of the polarized rays, but transmits both 
of them, calcite acts much like tourmaline. Do you recall 
now the change in color that occurs four times during 
rotation of a dichroscope? A section of calcite is called a 
mcol prism when used to polarize light in a microscope. 
Disks of Polaroid Film (Fig. 50) have the same tuV and 


are a less costly substitute for a natural mineral. A dichro- 
scope is superior for viewing the dichroism of gems, how- 
ever, because it shows the twin colors simultaneously 
(Fig. 48), no rotation being necessary to produce a change 
in color. 


Fig. 50 Polaroid Film in Crossed Position 

The vibration directions in the two disks are at right angles to each 
other. Any light that passes through the first disk is absorbed by the 
second. [Polaroid Corp.] 

We have seen that both rays of doubly refractive gems 
are polarized and travel in different directions, vibrating 
about at right angles to each other. Each vibration direc- 
tion has a different color absorption, producing dichroism. 
From these facts comes the need for the skillful cutting 
of nr < ^ -ms to yield the best color. The top facet of 


a cut ruby should be parallel to the top face of the ruby 
crystal for the stone to show the richest possible color. 
Tourmaline, on the contrary, is usually too dark in that 
orientation, and a more desirable color is obtained by cut- 
ting the top facet to correspond to a side face of the 

Unusual Effects 

A number of gems are so distinctive in their optical 
effects that descriptions are entirely inadequate to do them 
justice. To quote the classified ads, they "must be seen 
to be appreciated." Once seen, such gems can never be 
forgotten, and their recognition becomes largely a matter 
of having a typical specimen. 

These unusual phenomena are further discussed, together 
with an explanation of their cause, in later chapters, under 
the descriptions of the individual gems. 

The reflection of light from enclosed substances ar- 
ranged in certain crystal directions within a gem gives 
rise to asterisinrxys of light extend in starlike fashion 
across the rounded surface. Star ruby and star sapphire 
are the best-known examples, though the same property 
is also seen in some other gems, especially garnet and rose 

A parallel alignment of mineral fibers causes the related 
condition of chatoyancy, which is conspicuously seen as 
a band of light in such gems as cat's-eye (both the chryso- 
beryl and quartz varieties), tiger's-eye, and hawk's-eye. 

More spectacular even than these are the effects that 
come from the interference of light. The magnificent 
play of pure color that is the splendor of opal, the vivid 


sheets of color that sweep across the face of labradorite, 
and the charming blue sheen of moonstone are alike caused 
by the conflict of light rays which mingle as they are 
reflected from thin films and crystal plates within the gem 
and near its surface. 


The amazing effects of ultraviolet light, transforming a 
mineral cabinet into a fairyland of color, are among the 
interesting studies of modern gemology. The meaning of 
luminescence, fluorescence, and phosphorescence their ori- 
gin, description, and value in helping to recognize gems- 
are discussed in Chapter 8. 


As explained previously, a consideration of the physical 
properties of gems may include those that are optical in 
nature or optical properties may be given separately. The 
second procedure has been followed in this book, and the 
purely physical properties that do not deal with light will 
be presented next. 

Weight and Specific Gravity 

Gems are usually weighed in carats. Before the uni- 
versal adoption of the metric carat, which was legalized in 
the United States in 1913, the unit of weight used by gem 
dealers varied from country to country. A carat was 
originally the weight of a seed of the carob or locust tree, 
native to the Mediterranean region. (The word karat is 


quite different and refers to the purity of gold alloy.) The 
present carat equals one-fifth of a gram, and about 150 
carats are equivalent to an ounce. Each carat is divided 
into 100 parts called points, as a dollar is divided into 100 
cents. Gems of lesser value may be sold by the gram, 
pennyweight, or ounce, or occasionally in larger units. 
Some cut stones are priced according to size, measured in 
millimeters or inches. Pearls, on the other hand, are sold 
by the pearl grain, four of which are required to make a 

Those who handle gems soon recognize that some gems 
weigh more than others that have apparently the same size. 
A one-carat diamond is too large to fit in a ring mounting 
prepared for a one-carat zircon. To express it another way, 
a diamond and a zircon of the same dimensions have dif- 
ferent weights. A zircon simply is heavier than a diamond 
with the same external measurements; zircon is denser or 
(as we say) has a greater specific gravity, meaning that it 
weighs more than an equal volume of diamond. This is 
due mostly to the fact that the elements of which zircon 
is composed (zirconium, oxygen, and silicon) have greater 
atomic weights than the single element (carbon) in 

Complicated measurements or special equipment would 
be necessary to determine the volume of a gem, but when 
all gems are compared in density with water, the actual 
procedure for the determination of specific gravity be- 
comes a fairly easy matter. Because most gems are pure 
substances, their specific gravity is quite constant. Calcu- 
lating it provides a good way to distinguish between gems 
that have the same appearance. They may be of any size 
or shape, rough or cut, as long as they are unset. 

A cubic centimeter of cold water weighs a gram. All 
genjs are heavier than water, but they weigh less when 
suspended in water than they do in air, as a swimmer 
weighs less under the same circumstances, because he has 
displaced his own volume of water and is buoyed up by 
a force equal to the weight of the water that he displaces. 
The amount by which the gem decreases in weight is 
equal to the weight of the displaced water and indicates 
its relative density. The formula to be used involves two 
weighings; the weight of the stone in air is divided by 
the loss of weight in water. The specific gravity of dia- 
mond is 3.52, that is, it weighs a little over three and one- 
half times as much as the same volume of water. For this 
test the gem may be held in a coiled wire hung from a 
jeweler's balance. Specific gravity apparatus can be pur- 
chased if desired but home-made equipment is usually 

Heavy liquids are often more convenient than scales. 
They make use of the principle that a gem will remain 
suspended in a liquid of the same density, will sink in a 
lighter liquid, and will float in a heavier one. Several 
chemicals are available for this purpose; bromoform, 
methylene iodide, and Clerici's solution are most often 
used. The simplest test of this kind requires only a glass 
of strong salt water in which amber and other natural 
resins float, whereas their plastic imitations (such as bake- 
lite) drop to the bottom. By mixing several liquids, a 
diffusion column, which becomes heavier toward the lower 
part, can be prepared; a number of gems can be suspended 
in it at the same time, resting at different levels according 
to their specific gravities. Known gems called indicators 
"sed for comparison. Porous gems, including opal, 


Specific Gravity Table 

Cassiterite 7.00-6.80 

Hematite 5.15-4.95 

Pyrite 5.02-4.84 

High zircon 4.72-4.68 

Spessartite garnet 4.20-4. 1 2 

Almandite garnet 4.20-3.90 

Low zircon 4.10-3.94 

Corundum 4.01-3.99 

Spinel 3.98-3.58 

Andradite garnet 3.86-3.82 

Pyrope garnet 3.82-3.68 

Grossularite garnet 3.80-3.60 

Chrysoberyl 3.72-3.70 

Topaz ' 3.58-3.50 

Diamond 3.53-3.51 

Olivinc 3.50-3.32 

Jadeite jade 3.36-3.30 

Spodumene 3.23-3.17 

Fluorite 3.18 

Tourmaline 3.12-3.00 

Nephrite jade 3.02-2.90 

Lapis lazuli 2.90-2.70 

Beryl 2.85-2.65 

Turquoise 2.85-2.60 

Quartz 2.65 

Orthoclase feldspar 2.57-2.55 

Obsidian 2.47-2.33 

Opal 2.20-2.00 

Jet 1.34-1.30 

Amber 1.09-1.05 


turquoise, and pearl, should not be immersed in strong 
chemicals, and this test is not suitable for them. 

Amber is the lightest gem; hematite and cassiterite are 
the heaviest, though zircon has the highest specific gravity 
of the major precious stones. Frequent lifting of gems, 
small though they are, gives one a surprising ability to 
identify many of them by this property alone. Typical 
values, with the range taken from G. F. Herbert Smith's 
Gemstones, are given on page 54. 


The other essential attribute besides beauty and rarity 
that gives a substance value as a gem is durability the ca- 
pacity for standing up under the effect of abrasion, impact, 
and chemical action. Beauty, in other words, must be as 
permanent as possible. A few gems are always popular 
in spite of their lack of durability because their color is so 
pleasing. The two physical properties which determine 
the durability of a stone are hardness and toughness. These 
are often confused even by lapidaries. Hardness, as will 
be explained, is simply resistance to scratching; toughness 
or tenacity is resistance to breakage, either by cleavage, 
parting, or fracture. The property that combines both 
hardness and toughness is called cohesion, which is the 
force of electrical attraction that resists separation of the 
atoms and the ions. 


Hardness contributes greatly to the beauty of a gem, 
as well as to its durability. The brilliant luster that is so 


attractive a feature of diamond is largely made possible 
by the permanent polish that can be given to the stone. 
As everyone knows, diamond is the hardest of all sub- 
stances and will scratch anything else. Designating dia- 
mond at one extreme as number 10, and the softest 
mineral, talc, at the other as number 1, a mineralogist 
named Frederich Mohs over a century ago proposed the 
scale of hardness still in common use. Here it is: 

10 Diamond 5 Apatite 

9 Corundum 4 Fluorite 

8 Topa/ 3 Calcite 

7 Quartz 2 Gypsum 

6 Feldspar 1 Talc 

This scale is often misunderstood; it indicates the rank 
of hardness but not the amount of hardness. The tenth 
stone (diamond) is not twice as hard as the fifth (apatite), 
nor is number 9 (corundum) three times as hard as number 
3 (calcite). In fact, the difference between diamond (10) 
and corundum (9) is far greater than the interval between 
corundum and the bottom of the series. What the table 
means is that a mineral will scratch any other listed below 
it, and will in turn be scratched by all those above it. 

Number 7, quartz, marks a natural division between the 
harder and softer gems, because the dust and grit in the 
air contain countless particles of sand, which is pulver- 
ized quartz. Thus stones softer than number 7 will be- 
come dull with daily wear, losing their luster and their 
splendor, though opaque stones do not show the effect as 
conspicuously as transparent ones. It is desirable to re- 
member, however, that the surface of most gems can be 
inexpensively restored by repolishing. The softer stones 


are quite satisfactory for neck and brooch ornaments since 
these are not subject to frequent abrasion. As contrasted 
both with natural stones and with their synthetic counter- 
parts (which are very hard), the chief objection to glass 
imitations has always been the ease with which they be- 
come scratched and rounded after a little wear. 

The hardness of crystalline gems varies with the crystal 
direction. In most stones these variations are of little con- 
sequence. One gem, kyanite, is so amazingly constituted 
that it can be scratched by a knife along the "grain" but 
not across it. The hardness of diamond depends upon the 
distance between the carbon atoms (the atomic structure 
is shown in Fig. 1), and study has shown the easiest direc- 
tion for cutting to be parallel to a crystallographic axis. 
Inasmuch as each cube face is parallel to two axes, facets 
that are cut in that direction yield most readily; octahedron 
faces are equally inclined to all three of the axes but are 
parallel to none and so present the greatest opposition. 
Any difference in hardness among diamonds from dif- 
ferent localities, especially Australia and Borneo (as stated 
by cutters), seems to be due to twinning or other irregu- 
larities in the structure rather than to variations in the 
actual diamond substance. 

The hardness of practically all the gems except kyanite 
is characterized by its essential constancy; hence hardness 
would be one of the most useful tests for determining the 
identity of a gem except for the fatal drawback that a 
scratch may harm a cut gem, perhaps even setting up 
stresses that will eventually cause it to split. An imitation 
stone, attractive though it may be, is especially likely to 
become disfigured, and other tests have largely superseded 
the one for hardness. . If the test is necessary, however, 


Hardness Table 

Diamond 10 

Corundum 9 

Chrysoberyl 8% 

Topaz, spinel 8 

Beryl, almanditc garnet 7% 
High zircon, pyrope garnet, grossu- 

larite garnet, spessartite garnet 7% 

Quartz, tourmaline, jadeite jade 7 
Andradite garnet, olivine, nephrite 

jade, spodumene 6% 

Opal 6 1 /{>-5% 

Feldspar, turquoise, low zircon 6 

Lapis lazuli 5% 

Sphene, apatite, variscite, obsidian 5 

Fluor malachite 4 

Coral 3% 

Pearl, sphalerite 3% 

Jet 3 

Amber 2% 

Gypsum 2 

the least conspicuous place on the gem should be selected; 
this is usually the widest part, called the a girdle," which 
can be covered later by the mounting. Care should be 
taken also to avoid mistaking the scratch from a harder 
substance for the powder left by a softer one. It is safer 
to use the unknown gem to scratch the other. Note 
should be made of the ease with which the scratch is se- 
cured; diamond, for instance, will gouge a ragged hole in 
a fragment of glass, whereas some other gem may produce 
only a fine line. Rough gems and crystals are quite ap- 
propriately tested for hardness, and for this purpose a set 


of standard mineral fragments, known as hardness points, 
may be advantageously used. Convenient approximations 
for hardness are made with the finger nail (2% in the 
scale), a copper cent (3), a piece of window glass (5%), 
a knife blade (6), and a steel file (6Vo). 

The hardness of most of the important gems is given in 
the table on page 58. 


The infinitesimally small particles of which gem crystals 
are built are arranged in definite layers in three dimensions 
and are held together in their specific structural pattern or 
"lattice" by electrical attraction. Where the cohesion be- 
tween layers is weakest, the stone under pressure or a blow 
will split in regular directions along its "grain" this split- 
ting is known as cleavage. In gems it can occur only in 
those that are crystalline minerals. Cleavage planes are 
always parallel to possible faces of the crystal; if such 
faces are not actually present, at least they may exist on 
some other crystal of the same species. Cleavage is often 
recognized by steplike chips on the surface of a gem or by 
(parallel cracks in the interior. Even the kind of cleavage 
may sometimes be determined from the shape of these 

Cleavage is described according to its quality and its 
direction. Thus "perfect octahedral" cleavage (typical of 
diamond and fluorite) is parallel to the octahedron faces 
in the isometric system and gives smooth, bright surfaces 
with facility. Again, "indistinct prismatic" cleavage yields 
an uneven surface roughly parallel to a prism face. After 
one becomes familiar with the "habits," or common forms, 


of crystals, he may sometimes recognize them in cut gems 
from the angles made by cleavage cracks. 

The ready cleavage in diamond is utilized for splitting 
the crystal into convenient pieces for cutting. (See Fig. 
63.) Topaz has a remarkable cleavage parallel to the base 
of the crystal, so that it can be split into thin plates more 
easily than a loaf of bread can be sliced. Kunzite (the lilac 
variety of spodumene) is exceedingly fragile because of its 
delicate cleavage in two directions; cutting a finished gem 
is a real triumph of the lapidary's art. Feldspar also cleaves 
in two directions almost at right angles to each other. 


A sort of "false cleavage" is known as parting, and is 
usually due to minute secondary twinning. It is especially 
evident in corundum, which has a tendency to split in two 
directions, one of which is parallel to the base of the ruby 
or sapphire crystal, the other being inclined in a rhombo- 
hedral plane. Corundum separates, however, only in cer- 
tain layers at definite intervals. This behavior distinguishes 
parting from true cleavage, which would take place along 
every layer in such directions. 


Amorphous gems have no cleavage and can break only 
with a fracture, which consequently has no regular direc- 
tion. Crystalline gems may have both cleavage and frac- 
ture, although a strong cleavage tends to predominate over 
a possible fracture. Emerald is a conspicuous exception 


because it fractures without difficulty but does not or- 
dinarily cleave. 

Fracture is described according to its appearance. The 
most distinctive variety in gems is conchoidal (Fig. 51), 
meaning shell-like, resembling the concentric arcs on shells 
and chipped glass. Quartz is characterized by this kind of 

Fig. 51 Conchoidal Fracture in Obsidian 

[From Longwcll-Knopf-Flint Outlines of Physical Geology, 2nd 
edition, copyright 1941.] 

fracture. Other fracture surfaces are called splifitery, 
uneven, and even. 

The difference between hardness (resistance to scratch- 
ing) and toughness or tenacity (resistance to breakage) is 
shown by a number of hard stones, such as topaz and 
emerald, which are fragile and will shatter if struck. Most 
zircons (especially the popular blue, colorless, and golden 
ones), though reasonably hard, are brittle as a consequence 
of the heat treatment given to improve their color, and 
hence they have an unfortunate disposition to chip around 
the edges. 


In contrast to gems that are rather easily cleaved or 
fractured, there are some that are tough in all respects. 
Jade is no harder than quartz, yet, because of its matted 
structure, a slab of it can be hurled against a wood floor 
without damage. 


The word electricity comes from the Greek word for 
amber, which the Greeks called elektrow. The ability of 
amber after being rubbed to attract light fragments of 
material was noticed as early as 600 B.C. Other gems also 
develop enough static electricity by friction to catch small 
bits of paper. Diamond, tourmaline, and topaz show well 
this interesting property. Most gems must be polished 
in order to exhibit positive frictional electricity; diamond 
is practically the only exception and is positive whether 
rough or cut. Gems, except the few metallic ones, are 
nonconductors of electricity. 

Tourmaline was brought to the attention of the Western 
world when some Dutch children found that the sun- 
heated stones attract and repel ashes and straws. Tour- 
maline was thus found to develop positive and negative 
electricity at opposite ends. The poles reverse them- 
selves when the stone cools. Some jewelers have noticed 
that tourmaline jewelry displayed in warm windows be- 
comes dustier than other kinds; this pyro electricity is the 

Similar u polar" electricity is called piezoelectricity when 
the accompanying change in volume is caused by pressure 
instead of heat. Tourmaline crystals are used in sub- 


marines to register depth electrically because of their sen- 
sitivity to slight changes in pressure. 

Reversing the procedure by the application of an alter- 
nating current of electricity to tourmaline causes it to 
change volume with such rapidity that it vibrates at high 
frequency. When the current corresponds to the natural 
frequency of the mineral, the vibration is greatly magni- 
fied. Plates of quartz, properly oriented and cut to proper 
thickness, vibrate with remarkable constancy. They are 
employed to maintain the wavelength of radio broadcasts. 
The variety and extent of their use for frequency control 
in electronics underwent a phenomenal growth during the 


An extremely delicate sense of touch is required to iden- 
tify a gem by its texture. However, several of the min- 
erals commonly used in carvings as substitutes for jade 
can be recognized in this manner. Steatite (soapstone) 
and agalmatolite are the best known; their softness causes 
them to feel soapy. Topaz seems to some persons to have 
a distinctive slippery feel which they ascribe to its won- 
derful polish. 


Heat may be considered physical or chemical in effect 
physical, when variations in temperature cause expan- 
sion and contraction which lead to breakage; and chemical, 
when some change occurs in the composition of the sub- 


stance. Excessive heat will damage many gems by enlarg- 
ing flaws or even creating them. At other times the color 
may be temporarily or permanently altered. 

Opal contains a considerable amount of water and will 
crack as it dries; desiccation may be prevented by keeping 
it covered with a thin film of olive oil. Jewelers in dry 
climates, as in the American West, are familiar with this 
useful suggestion, and some of the finest opals ever sold 
in this country have been kept in oil swathes. 

Tests involving heat are, for obvious reasons, even more 
limited than chemical tests in their application to gems. 
The blowpipe tests that are widely used in determinative 
mineralogy are suitable only for fragments. There are 
two gems, however, that may in uncut form be partly iden- 
tified by the use of a simple flame. A rough piece of jet 
may be tested by holding an edge of it in the flame, which 
it makes sooty. Amber under the same conditions gives 
off an aromatic odor, as do several of its chief natural sub- 
stitutes, though not the plastic imitations. 

Minor Properties 

Occasionally other properties besides those already dis- 
cussed are of value in recognizing gems. Some of them 
occur rarely, but when observed they indicate with cer- 
tainty the identity of the gem. Almost every precious 
stone has some characteristic that usually becomes familiar 
only after much experience in handling gems. Many such 
peculiarities represent delicately balanced combinations of 
optical properties. Others are structural or are due to the 
enclosure of foreign materials. The descriptions o indi- 


vidual gems in subsequent chapters of this book tell how 
their distinctive appearance is an aid to easier recognition. 


Gems, like people, are known by the company they 
keep and the homes they live in. So typical are the rock 
and mineral associates of some gems that the discovery of 
one of them invites a thorough search for the others. In 
1870 the first diamond ever found in its original rock was 
discovered, and an ancient continent came to life again, 
because a man named DeKlerk noticed some garnet pebbles 
in. a dusty South African stream bed and knew that the 
two gems are often found together. Suites of minerals, 
called satellites, accompany diamond in each of its locali- 
ties. In river deposits they are sometimes referred to as 
bantams. Some of the minerals are themselves gemstones. 
Pyrope garnet, olivine, diopside, and zircon occur with 
diamond in the African pipes, and agate and olivine are 
typical of the stream deposits. Quartz, garnet, tourmaline, 
zircon, and corundum are found in the Brazilian diamond 
fields, where they are called favas. 

Gems are formed in a variety of ways. Their history 
is a dramatic chapter of earth lore. To the creation of a 
mountain range, the eruption of a volcano, the bubbling 
of a hot spring, the flow of lava, the burial of a forest, 
even the crash of a shooting star to each of these geo- 
logic events, and to others as well, gems owe their ex- 
istence. Some modes of occurrence are, of course, more 
important than others. A knowledge of the types of rock 
in which a given gem is found often assists in recognizing 
it. The history of gem mining bears out Sydney H. Ball's 


observation that "gem discovery has progressively become 
less a matter of chance and more a result of trained tech- 

Three main kinds of rock igneous, sedimentary, and 
metamorphic together constitute the outer part of the 
earth, called its crust. 

Igneous rocks are formed by the cooling and solidifica- 
tion of magma, which is a hot solution of liquid and gas. 
When magma remains buried deep within the earth it loses 
heat slowly, and crystals are given sufficient time to grow 
to a visible size. On the contrary, when magma does not 
harden until it is close to the surface, or until it actually 
flows out upon the ground as lava, it cools too rapidly to 
yield conspicuous mineral grains; the final rock may be 
merely a natural glass such as obsidian. In either event 
the precise name of the rock produced depends upon its 
mineral and chemical composition, texture, color, and still 
other factors. 

Kimberlite, the diamond-bearing rock of the South Afri- 
can volcanoes, is referred to as a basic igneous rock because 
it contains no quartz. Acid igneous rocks, on the other 
hand, contain specimens of quartz, enough surplus silica 
having been present to crystallize by itself. 

In connection with deeply formed igneous rocks are 
pegmatites. To avoid confusion over the exact technical 
meaning, which has never been entirely agreed upon, it is 
adequate to say that pegmatites are the rocks (usually re- 
lated to granite) that are noteworthy for their coarse 
texture and large crystals. They are probably the last 
part of a molten mass to solidify and they retain to the 
end considerable amounts of steam and other gases. When 
such rocks have penetrated cracks in adjacent rocks they 


are known as pegmatite dikes or veins. Many rare min- 
erals, including a wide variety of the most interesting 
gems, are found in pegmatites. For some gems, including 
rose quartz, moonstone, and smoky quartz, pegmatites are 
the only original source; for others, such as spodumene, 
they are the only important source. Because thick veins 
of white quartz often indicate the proximity of pegma- 
tites, to which they arc related, their existence should be 
noted at least with curiosity. 

Even deeply buried rocks are at last uncovered by the 
forces of erosion. Sedimentary rocks, the second chief 
type of rock, are secondary in origin, having been derived 
from the decay and disintegration of earlier rocks. The 
weathered particles are carried by wind and glaciers, but 
mostly by streams, and deposited in layers. These sedi- 
ments may settle out because of their weight, or they may 
be chemically precipitated out of solution. 

Igneous or sedimentary rocks that have been consid- 
erably altered by heat, chemical reaction, or pressure be- 
come tnetaworpbic rocks, the third main kind of rock. 
These may in turn become sedimentary rocks by being 
broken down, carried away, and redeposited. Garnet, 
lapis lazuli, and jade are among the typical metamorphic 


Gems may be found in the rocks in which they were 
formed. The rocks must be mined to recover the precious 
contents. Diamond pipes, emerald veins, jade quarries, 
and pegmatites are examples. 

When gems are washed out of their native rock and 
transported by streams, their durability preserves them 
until they eventually come to rest, together with metals and 
other heavy minerals, as placers or gravel deposits. Such 


sedimentary deposits usually yield gems with less cost and 
danger of breakage than hard rocks. Placers also have the 
advantage of high concentration, which makes them more 
profitable to operate. The rich and varied gem gravels of 

Fig. 52 Large Geode Lined with Gem Crystals 

[Ward's Natural Science Establishment.] 

Ceylon, the alluvial diamond beds of Africa, and the sap- 
phire fields along the Missouri River in Montana are typical. 
Ocean waters have concentrated amber along the shore of 
the Baltic Sea and diamonds on the west coast of Africa. 
Geodes (Fig. 52) are cavities, caves, or hollow rocks 
lined with minerals, including quartz, opal, and chalcedony, 


which have settled out of solution. The myriad of small 
bright crystals nestling among larger ones aptly fit John 
Ruskin's description of "courtier crystals glittering in at- 
tendance upon others/' 

The evaporation of hot silica waters, such as flow from 
some springs, may leave gelatinlike material in the form of 
opal or chalcedony. Descending rather than rising mineral 
waters deposit turquoise in cracks in rock. Amber and 
jet, both gems of vegetable origin, are found in ancient 
sedimentary beds, where they were imprisoned for future 

A number of gem minerals, especially olivine and dia- 
mond, come to the earth in meteorites. 

Climate plays a part in the occurrence of some gems. 
Turquoise may be looked for profitably only in dry re- 
gions, close to the surface of the ground. Olivine is so 
readily altered under atmospheric conditions that it is 
found only in fresh rock or as residual grains in desert 
country. Coral is notoriously sensitive to its environment, 
and water of constant temperature is requisite to its growth. 
The other gems of organic origin are also dependent on 
the factors that govern the growth of living things. 


Chapter 3 

Faceted Gems 

John Ruskin expressed the point of view of the purist, 
and of the mineralogist as well, when he disapproved of 
disfiguring any crystal by subjecting it to the cutting and 
polishing process. But rare is the gem that cannot, for 
jewelry purposes, be improved in beauty through adequate 
lapidary treatment. 

Pearl and staurolite are the only gems, in fact, that are 
worn in their natural state; however, the former is usually 
pierced for stringing into beads and the latter for hanging 
on a chain. Thus the art of the lapidary is involved in 
some manner in the use of all gems. This art at times be- 
comes a science, dependent upon mathematical relation- 
ships which only secondarily have aesthetic significance. 

In certain respects, moreover, the value of gems is 
largely determined by the perfection of their cutting. 
Poor work may ruin the finest stone, whereas skillful exe- 
cution shows many inherent possibilities to best advantage. 

Gems are classified in this book according to the style 
of cutting facet or cabochonto which they are most 
suited. Faceted ge?m y discussed in this chapter, are char- 
acterized by smooth flat surfaces or facets (from the 


French word meaning "little face"). Cabochon gems 
(frgm the Latin word caput meaning "head") have 
rounded surfaces of varying degrees of curvature; the 
extension of the surfaces completely around a stone forms 
a bead. Combinations of both plane and rounded surfaces 
are also known. There are, in addition, carved and en- 
graved stones fashioned as cameos, spheres, ornaments, and 
many other forms. Examples of the ingenuity that even 
an amateur lapidary may display are shown in Fig. 53. 

Almost every gem appears in both major types of design. 
In general, transparent gems, whose beauty lies in their 
clearness, brilliancy, and fire, are selected for faceting, for 
only in this way are the desired properties fully revealed. 
The cabochon cuts, on the contrary, are more effective 
for opaque or translucent gems which have a pleasant color, 
show interesting mottling or markings, or possess unusual 
optical effects. 

Ludwig van Berqtiem, of Flanders, is said to have discov- 
ered in the 15th century the advantages of placing sym- 
metrical facets on diamond. Before that time cutters 
limited their efforts to covering the surface at random with 
many small flat patches, mostly for the purpose of con- 
cealing flaws. For approximately one hundred years, two 
styles of fashioning predominated the diamond point, in 
which only the natural faces of the octahedron were pol- 
ished, and the table cut, a more elaborate pattern also 
adapted from the original form of the crystal. 

The rose cut, developed in a number of outlines, most 
of them with triangular facets, further improved the ap- 
pearance of gems. It was regarded as quite satisfactory 
until the close of the 1 7th century, when Vincenti Peruzzi, 
of Venice, introduced the brilliant cut, which has, with 


O ^3 















gradual minor changes, remained the standard for diamond 
cutting ever since. It revolutionized the gem industry 
by bringing out the real beauty of diamond and the bril- 
liancy of other gems. At present the brilliant cut has 58 
facets, 33 above the circular u girdle" and 25 below it, 
arranged in 8-fold symmetry. The names of the individual 
facets vary in different countries and languages. This 
style is the only one that has a scientific basis and is fully 
adequate to the optical properties of highly refractive 
stones. The American cut, planned originally by Henry 
Morse of Boston, is regarded as the most effective modi- 
fication. Within the past few years several firms in the 
United States have publicized, under such names as Multi- 
Facet, Magna-Cut, and King-Cut, the cutting of diamonds 
with numerous additional facets and a polished girdle. 

When the outline of the brilliant cut is altered to meet 
the requirements of modern jewelry such forms as the 
boat-shaped marquise and the pear-shaped pendeloque are 

Colored gems are often cut in a generally square shape 
with a series of parallel facets leading both up and down 
from the girdle. Known as the step, trap, cushion, or 
emerald cut, this pattern is especially well suited to emerald, 
and many fine diamonds are cut similarly. Possible vari- 
ations yield angular stones that are easily adaptable to 
current tastes. These have such descriptive names as ba- 
guette, trapeze, epaulet, lozenge, and keystone. 

A distinction is made in the gem-cutting industry be- 
tween shops that cut diamonds and those that fashion the 
other stones, since there is a vast difference in the hardness 
of the materials and the skill required. The technique of 
the lapidary, including his machinery, tools, and methods, 


are explained in the third edition of The Art of Gem Cut- 
ting by Dake and Pearl. 1 Equipment for polishing flat 
surfaces on "slabs" is shown in Fig. 54, and Fig. 55 illus- 
trates an adjustable holder for cutting facets. 

The species of gems that are customarily cut in facet 

Fig. 54 Lapidary Apparatus for Polishing Flat Surfaces 

[United States National Museum.] 

style are described in the rest of this chapter. Their se- 
quence follows the arrangement of minerals given in the 
seventh edition of Dana's System of Mineralogy. 2 

1 Mineralogist Publishing Company, Portland, Oregon, 1945. 
2 Palache, Berman, and Frondel, Harvard University. Published by 
John Wiley and Sons, Inc., New York. Volume I, 1944. 



It was during the age of dinosaurs, about 60 million 
years ago, that a subterranean drama was enacted which 
was to change the history of the African continent. Ac- 

Fig. 55 Mechanical Device for Faceting Gems 

[M. D. Taylor.] 

companied by violent explosions, enormous amounts of 
diamond-bearing volcanic rock were propelled upward, 
perforating the earth, which gave way before the irre- 
sistible force, and shattered rock filled the newly formed 
fissures. Then the vigorous underground activity ceased, 


but through succeeding ages the rain pelted down and the 
wind hurled itself against the ground, until, at the advent 
of man, all previous landscapes had long since disappeared, 
and in their place was the parched, monotonous African 
veldt, stretching in limitless desolation from rising to set- 
ting sun. Neither the natives nor the white man saw any- 
thing remarkable about the land, and farms were laid out 
and homes built in the few places where pioneers settled 
with their families. Diamonds to them were merely ex- 
pensive baubles worn by the rich luxuries associated with 
the splendor of the Orient, the refulgence of India, and 
the remoteness of Brazil. Nothing to interest hard- 
working Boers, thought they; so on they worked, and 
cleared their ground, and reared their children, and 
despised their English neighbors. 

In 1867, while visiting some friends, Schalk van Niekirk 
was attracted by an unusual stone lying on the floor of 
the farmhouse and offered to buy it. He was laughingly 
told that it was but a child's plaything picked up in the 
field and that he should take it with him. Some time later 
the stone was shown to a mineralogist who identified it 
as a diamond worth several thousand dollars. There fol- 
lowed eager prospecting for other odd pebbles, but none 
was found for two years, until a shepherd boy discovered 
the magnificent "Star of South Africa," which he traded to 
van Niekerk for 500 sheep, 10 oxen, and a horse. It was 
later resold for $125,000. 

Now began a wild diamond rush, as frantic and frenzied 
as any search for gold or oil. It centered about a number 
of places, first along the rivers and then inland where de- 
posits were found in solid rock. The richest of these 
fields were the most crowded, and as the digging contin- 


ued unabated the walls of the mines collapsed with ensuing 
death and terror. Order was finally restored by the action 
of several men who formed a combination by buying up 
the titles of the individual miners; this diamond trust- 
under the leadership of Cecil Rhodes, able successor to a 
long line of British empire builders became one of the 
most powerful of the world's industrial corporations with 
vast ramifications under the beneficent stewardship of the 

There are three distinct layers of rock in diamond mines. 
The tt>p stratum is the yellow ground, so called from the 
color produced by oxidation, the cause of the decomposi- 
tion that renders it easy to work. Beneath, of varying 
depth, is the blue ground; it has undergone partial altera- 
tion, weathering uniformly throughout, and disintegrates 
upon exposure to air, wind, and rain for about a year and 
frees its gemmy treasure. The blue ground is sometimes 
pierced by veins and dikes of hardebank, the third and 
least productive layer. The richness of the earth gradually 
diminishes; because the yellow ground has been depleted 
and the hardebank will not pay expenses, practically all 
the mining is done in the blue ground. 

Shafts are sunk parallel to the pipe (as the neck of the 
former volcano is called; see Fig. 56) and tunnels are dug 
until they reach the pipe. The common operations in- 
volved in mining drifting, stoping, drilling, blasting, slic- 
ingare used. Piles of rock are then loaded (Fig. 57) onto 
trucks, each carrying 20 cubic feet, and moved over nar- 
row rails to the storage bin, to be transferred later to the 
elevator or "skip" and raised to the top (Fig. 58). 

Although, as mentioned, the blue ground yields its 
minerals after exposure to the weather and this method of 




r ^ 

. o 

g 8 


E c 


o 8 



Fig. 57 Kafirs Loading Blue Ground 

Fig. 58 Washing Plant and Tailings Dump 
Diamond Mining at Dutoitspan 


"farming" is used especially during times of depression 
a more direct operation is available to hasten the day when 
the stones can be placed upon the market. The diamond- 
bearing rock is rolled and crushed in the jaws of great 
presses; then it is screened through coarse wire nettings 
which successively decrease in size until the material is no 
larger than a walnut. This is put into great circular wash- 
ing pans, in which it is revolved and hurled against notched 
barriers which thrust the heavy minerals to the bottom, 
while the water and sand are drawn off through openings 
in the sides. After another series of screenings, the mate- 
rial is taken to the "jigs" or pulsators, in which the heavy 
minerals meaning the valuable ones are forced by plung- 
ers (see Fig. 59) through a layer of gravel which the lighter 
material is unable to penetrate. 

The remaining concentrate is then fed to the grease 
tables (Fig. 60) slanted, rectangular sheets of metal, cov- 
ered with a layer of petroleum jelly, and vibrating from 
side to side. The value of these tables lies in a peculiar 
property of diamond, which adheres immediately to grease 
but is untouched by water; as the stones roll down the in- 
cline, the diamond crystals are quickly caught, while the 
waste slides by, joining the "tailings" on the dump (Fig. 
58). At intervals the tables are scraped clean and the dia- 
monds are released by boiling, to be taken under guard 
to the offices, where they are sorted and graded for sale. 
Only an extremely minute portion of the blue ground finds 
its way here, for the richest mine ever known yielded at 
depth barely one part of diamond to 8 million parts of 

But a rough diamond is hardly worth going into ecstasies 
about, and the young man who attempted to present one 


Fig. 59 Rotary Washing Pan 
The heavy minerals arc separated from the sand. 

Fig. 60 Grease Table 

Diamond is the only mineral caught by the grease. 
Diamond Concentrating Methods 


Fig. 61 Marking 

Fig. 62 Notching 

Early Steps in the Diamond Cutting Process 



Fig. 63 Cleaving 


Fig. 65 Romulino 

Fig. 66 Faceting 

Later Steps in the Diamond Cutting Process 

84 [DeBeers.] 

Fig. 67 Sorting Diamonds 

Fig. 68 Ten Days' Production 



to the lady of his dreams would be fortunate to escape with 
minor cuts and abrasions. A well-designed diamond is a 
scientific as well as an artistic achievement; the facets must 
be of a certain number and of a definite size and shape, 
each bearing to the others a relationship determined by the 
laws of optics. Indian lapidaries were the first to fashion 
diamonds, but they merely removed the outer "skin" from 
the natural crystal faces or added small facets to disguise 
the presence of flaws. 

Five major steps are involved in the cutting process, and 
all must be done by experts, specialists in their work. The 
least spectacular phase, but in some ways the most im- 
portant, is done by the marker, who outlines in india ink 
(Fig. 61) those parts of the crystal which are to be re- 
moved and those which are to be utilized, according to the 
size, shape, color, and quality of each stone. After notch- 
ing (Fig. 62), the first shaping is done by the cleaver, who 
makes use of the pronounced cleavage, by means of which 
diamond may be split easily (Fig. 63) in any one of four 
directions. Cutting against the grain requires the work of 
the sawyer, who places the stone in a shell-like holder called 
a u dop," and slits it with a speedily revolving bronze disk 
covered with a mixture of diamond dust and oil (Fig. 64). 
The rough stone is then given a circular form by the cutter, 
who sets it in a lathe and rounds off the edges with a 
diamond-pointed tool (see Fig. 65). The facets are placed 
on the stone by the polishers, who work in turns, the first 
group shaping the 18 most important surfaces and the 
second group completing the other 40. Faceting is done 
on horizontally revolving iron wheels treated with the same 
compound of crushed diamond and oil that is used for 


sawing; the stone is held against the wheel by a dop set at 
the proper angle, as shown in Fig. 66. 

Inasmuch as diamond is cut so slowly that it polishes 
itself (the only gem that does) no further treatment is 
needed except cleaning in boiling acid. Only sorting (Fig. 
67) and marketing remain, although some dealers may 
assert that the latter is the most formidable task of all. 
There, in a folded paper, lies a thing of rare loveliness a 
mass of glittering light, a scintillating glow of varied colors, 
now separating into tints of spectral purity, now blending 
into the splendor of a twinkling star. (See Fig. 68.) It 
is a diamond, some day to be owned by an Indian maha- 
rajah, worn by an Knglish duchess, or placed on the left 
hand of an American girl. 

Alluvial Deposits 

The mining methods just described are employed only 
in the primary volcano or pipe deposits, which are rela- 
tively restricted in distribution. Prior to the discovery 
of the first pipe the world's supply of diamonds had 
always come from secondary sources shallow alluvial or 
placer deposits where the gems were concentrated with 
other heavy and resistant minerals in stream beds, river 
terraces, and sedimentary formations, mostly through the 
process of rock decay and the action of running streams. 
All the famed Indian and Brazilian fields had been sec- 
ondary sources. Upon the opening in 1926 and 1927 of 
several large African deposits in Lichtenburg and Little 
Namaqualand, the alluvial type again became the most 
important. During the past two decades alluvial mines 


have yielded all but a few per cent of the total (mostly 
now, however, outside the Union of South Africa). 

Obtaining diamonds from such surface workings is 
much simpler and less expensive than mining far under- 
ground. The deepest mine, the Kimberley, was operated 
below 4,000 feet, and even the most productive pipe con- 
tains diamonds only sparsely. Moreover, the alluvial stones 
are generally of better quality because those with the most 
flaws had been broken up during the journey from their 
place of origin. 

The alluvial deposits of Africa are widely scattered 
through the southern half of the continent. Some are 
located along the Atlantic Ocean beaches and may even 
have come from areas now buried beneath the sea. Angola, 
Sierra Leone, Belgian Congo, and Gold Coast fields con- 
tribute most of the alluvial diamonds; the Union of South 
Africa has lost its former predominance, although its placer 
and pipe mines combined give it first rank in terms of 
value. The Belgian Congo is, by weight, the largest pro- 
ducing country, but most of its output is industrial stones. 
One of the Bcceka mines is the richest in the world. An 
interesting feature of these alluvial fields is the presence 
of artifacts from primitive cultures, showing their geologic 

The Dutoitspan pipe mine was reopened in 1943 with 
the intention of working at least one mine of that type in 
prosperity and depression alike. The Bultfontein mine be- 
gan to operate the following year; the New Jagersfontein 
and Premier mines were announced in the spring of 1946 
as being made ready for production. The potential yield 
of the huge and much-publicized Williamson pipe in Tan- 
ganyika is still unknown. 


Indian Deposits 

India was the first source of diamond and from there 
have come most of the historically famous stones. Tradi- 
tion puts the discovery at about 5,000 years ago but that is 
probably twice as long as the actual time. The mines were 
exceedingly successful, reaching their peak in the 17th 
century; the marketing center was Golconda, a name 
which even today is a synonym for fabulous wealth. Gol- 
conda is now in the independent state of Hyderabad. 

Other Foreign Deposits 

As the yield in India rapidly declined virtually to the 
point of exhaustion, diamonds were found in Brazil about 
1720, and that country maintained its supremacy until 
surpassed by the African mines a century and a half later. 
The discovery of two new fields, enthusiastically reported 
in 1946 as the largest ever opened in Brazil, may indicate 
a revival of the industry there. 

Diamond is no stranger to still other countries. Notable 
stones have for a thousand years come from the western 
part of Borneo, where even during the Japanese conquest 
they were mined by Chinese and Malay prospectors from 
hundreds of small shafts in the jungle. Australian dia- 
monds have appeared at intervals from New South Wales. 
British Guiana fields promise much for the future when 
they become more accessible. Private capital is beginning 
to develop fields in Venezuela, where government plans 
for exploitation had previously failed. The Soviet Union 
may soon enter the ranks of the leading diamond-producing 
nations, but statistics are not available; the present output 


from the Ural Mountains is said to be twenty times the 
pre-war yield. 

United States Deposits 

Diamonds occur in Arkansas in a pipe that is remark- 
ably similar in structure and composition to those of South 
Africa. Many fine crystals, the largest weighing 40 carats, 
have since 1906 come from this area near Murfreesboro 
in Pike County. High cost of production has limited the 
output of the property, which is now leased by the Dia- 
mond Corporation of America (chartered late in 1945), 
but the United States Bureau of Mines has undertaken a 
prospecting and sampling project in an effort to secure a 
future domestic source of industrial diamond vitally needed 
in time of war. Occasional scattered diamonds have been 
picked up in a number of other states but their original 
source is unknown. The largest and most recent, an- 
nounced in 1943, is the 34-carat Punch Jones diamond, 
which was found in 1928 while a youngster and his father 
were pitching horseshoes in a vacant lot in Peterstown, 
West Virginia. 


Most of the diamond-mining companies of the world 
belong to the Diamond Corporation (known to most jewel- 
ers by its old name, the Syndicate), to which they sell 
their output. DeBeers Consolidated Mines, Ltd., is the 
largest supplier and also owns most of the stock. Each 
company has an allotted quota which is varied from time 
to time according to its prospects for production, so that 


the whole system of control is at once a strong and yet 
remarkably flexible monopoly. Not all these African com- 
panies are British, as is commonly believed, and some oper- 
ate on French, Belgian, and Portuguese territory. A few 
minor producers in other parts of the world do not belong 
to the corporation but often find it advantageous to co- 
operate in maintaining the price. Through its subsidiary, 
the Diamond Trading Company, the corporation disposes 
of the rough gemstones to brokers and cutters from offices 
in London and Kimberley. 


The word diamond comes from the Greek word mean- 
ing "unconquerable," referring to its extreme hardness 
and to the erroneous belief that it could not be broken. 


Diamond crystals show the common forms of the iso- 
metric system, corresponding to the atomic structure 
shown in Fig. 1. The most prominent forms are the octa- 
hedron (resembling a double pyramid), the dodecahedron, 
and the cube. The table of the cut stone is usually placed 
almost, though not exactly, parallel to a natural face of the 
crystal; and (as explained previously in the section on 
"Hardness") the easiest directions of cutting are those 
most nearly along a crystallographic axis. 

Diamond is crystallized carbon; the gem varieties are 
practically pure. Nothing in nature, however, is abso- 
lutely flawless and diamond is no exception. The flaws 
are usually spots of liquid compounds of carbon which 


failed to harden as the mineral was formed. In some 
stones, but in only about one per cent of the entire pro- 
duction, the flaws remain so small that they are not visible 
with a pocket magnifier. 

The other form of carbon is graphite, a mineral so dif- 
ferent from diamond that their relationship is almost un- 
believable. Graphite is the soft black substance used as 
pencil "lead," stove polish, and a lubricant, liven stranger 
is the fact that it is really the more stable form of carbon, 
because diamond changes to graphite at excessively high 

No property dependent upon the crystal structure of 
diamond is more interesting than the fact, which was dis- 
covered by the National Bureau of Standards in Washing- 
ton and reported in October 1947, that diamond can be 
used to measure the intensity of atomic radiation with great 

Famous Diamonds 

Through the display of glass replicas at world fairs and 
in jewelers' windows, the appearance and names of the 
famous diamonds of history have become popularly fa- 
miliar. Ten of the best known are pictured in Fig. 69. 
South Africa has furnished the largest stones, climaxed by 
the Cullinan, a giant of 3,025 carats, the size of a man's 
fist. A number of large diamonds, among which are sev- 
eral that have attained newspaper headlines, have been 
discovered during recent years. The Jonker, found in the 
Transvaal in 1934, had a superb clarity and weighed 726 
carats before it was cut into 20 stones. The Vargas dia- 
mond, named for the former president of Brazil, in whose 



Fig. 69 Some Famous Diamonds 

IN. W. Ayer and Son.] 


country it was found, exceeded the Jonker in weight by 
only 1 carat and was cut into 29 stones. The largest 
Venezuelan diamond is El Libertador, found in 1942 and 
named to honor Simon Bolivar, the liberator of most of 
South America; it has been fashioned into 3 emerald- 
cut stones. A diamond of 770 carats, the largest of all 
alluvial diamonds, was found in Sierra Leone, Africa, in 


Few diamonds are entirely devoid of color; those having 
a bluish tint are more desirable than yellow ones because 
of their greater rarity, although yellow diamonds are fre- 
quently more brilliant. The commercial term "blue white," 
so often misused today, properly means a gem showing no 
color in daylight except blue, and these are by no means 
common. Stones of a distinct hue, on the other hand, are 
called fancy diamonds and bring a good price. Red and 
deep blue are the rarest colors. The Moon of Boroda, a 
2 5 -carat pear-shaped canary diamond, brought to America 
from India in 1944, is the newest fancy diamond to be 
featured in the press. At the death of its owner, Evalyn 
Walsh McLean, in 1947 the fabulous blue Hope diamond 
(Fig. 69) was again brought to public notice. 

Cutting Centers 

The collapse of the diamond industry of the Lowlands 
was one of the dramatic events of the war. Antwerp in 
Belgium and Amsterdam in the Netherlands have for cen- 
turies been the chief cutting centers; Antwerp alone con- 


sumed more "rough" than the rest of the world. The Dia- 
mond Corporation had been careful to send few stones 
abroad after the war began. With the German invasion 
the situation was demoralized, though many of the cutters 
escaped and were mainly responsible for the rapid growth 
of the industry in a dozen other countries. Since the 
termination of hostilities the Belgian lapidaries are show- 
ing a remarkable economic recovery, but the Dutch have 
not been so fortunate. 

The United States, the Union of South Africa, and the 
Netherlands are today the chief cutters of large stones, 
and Belgium, Palestine, and Cuba cut most of the small 
sizes. Prices have advanced in accordance with the in- 
crease in labor costs in the new places; the smaller stones 
have risen by far the most. New York is the center of 
American production, and half a dozen other cities house 
important diamond-cutting plants. Aiechanization may de- 
termine the extent to which the United States can retain 
its present share of moderate-sized stones, although the 
large stones have been cut here profitably for many years. 

Industrial Diamonds 

The earliest industrial use for diamond was to cut other 
diamonds. The next use was for glass cutting. Today 
there are so many indispensable applications that our vast 
industrial machine would be practically halted without 
them. Most are used for truing grinding wheels; nothing 
else will so effectively dress wheels of emery, Carborun- 
dum, and cemented tungsten and boron carbides. Many are 
used to turn machine tools; the important development of 
the bonded diamond wheel for this purpose has occurred 


largely since the beginning of the recent war. Such wheels 
made it possible to grind American cartridge dies in one- 
third of the previous time. Tungsten for light-bulb fila- 
ments, copper, and other metals are drawn into wire 
through diamond dies. The electrical equipment of a single 
bomber may include 10,000 feet of wire, all of which must 
be drawn through diamonds. A diamond-die industry, 
which centered in France and Switzerland before the war, 
was hastily created in the United States to meet the emer- 
gency. Drilled diamonds are used also in oil nozzles for 
furnaces. Diamond core drills are important in mining 
and oil-well operations. Stoneyards employ steel saws up 
to seven feet in diameter and containing perhaps a thousand 
diamonds to cut granite and marble. Diamonds are also 
used in phonograph needles; in optical and dental drills; 
in etching tools for the artist; and for turning ivory, hard- 
wood, and plastics into a wide range of articles from bowl- 
ing balls to doorknobs. Strategic mineral, to be sure! 

During the war, profits from the sale of gem diamonds 
enabled the producers to maintain a lower price level for 
the much-needed industrial stones than if the mines had 
been operated for them alone. Except the small yield in 
Borneo and some smuggling from South America, the 
allied nations had almost complete control over the out- 
put of industrial diamonds. Since the spring of 1946 
the Diamond Corporation has sold its industrial stones 
through a new subsidiary, Industrial Distributors (1946), 

Three varieties of industrial diamond are known. Eort 
is an aggregate of many tiny crystals without definite 
orientation; this term is also loosely used for poor frag- 
ments of actual gem type. Carbonado or black diamond 


also has an aggregate structure but of a different kind and 
is highly valued for drills; it is found almost exclusively 
in Brazil. Ballas consists of a radial mass of small crystals, 
which is very durable because it does not cleave easily. 
Uniformity of grading the diamond powder used in cut- 
ting diamonds has been secured in the United States by 
the adoption in 1945 of Commercial Standard CS 123-45 
by the National Bureau of Standards. Scientists of the 
same bureau announced in 1945 that the speed of both 
cutting and sawing can be greatly accelerated, especially 
along the difficult octahedron direction, by placing a 
high-voltage bluish electric arc at the contact between the 
diamond and the wheel; the surface finish or polish has not 
yet reached the perfection demanded of diamonds for 


The origin of diamond is still a mystery. A number of 
elaborate theories have been propounded but none of them 
fits all the conditions known to exist in the pipe mines, 
which are the only certain original deposits. The par- 
ticular rock in which these mines are dug is called k'nuber- 
lite. The diamond crystals may have formed at great 
depths in some other rock, which became broken off or 
engulfed by the new volcanic material which then forced 
it upward. They may, however, have formed in the kim- 
berlite itself during or after its actual rise in the pipe. Or 
they may have been a part of the kimberlite when it was 
deep in the crust of the earth. 

Enormous amounts of heat and pressure have generally 
been assumed to be necessary for the creation of diamond. 


Most of the experimenters who have tried, always without 
success, to make the gem synthetically have put their faith 
in the development of pressure. Yet in his work with the 
meteorites of Canyon Diablo, Arizona, Dr. Harvey H. 
Nininger found small diamonds surrounding a cavity that 
could hardly have existed under any considerable pressure. 
Much more needs to be learned before the cause of dia- 
mond will be known, and several different explanations 
will probably be required to cover all the situations. 


Few persons would believe by eye examination alone 
that two stones of such contrasting colors as ruby and 
sapphire are alike in all other respects. One, vivid in flam- 
ing red; the other, restful in the lustrous blue of the twi- 
light sky both are varieties of corundum which differ 
mainly in color. When the red and the blue combine they 
form a violet or amethyst sapphire. Indeed, practically 
every hue has been found, and there may even be several 
colors in adjacent layers in the same crystal. Corundum 
is the mineral family or species; ruby and the many sap- 
phires are the varieties. 

Diamond is the only gem that is harder. Ruby and 
sapphire, possessing in addition to hardness the advantage 
of having absolutely no cleavage (though there is a part- 
ing) and showing but a slight tendency to fracture, are 
therefore about the most durable of ring stones. They 
are heavy gems, as their high specific gravity indicates. 
They are brilliant gems with a high refractive index. 

Chemically, corundum is an oxide of aluminum; traces of 


other metallic oxides furnish the wide range of colors. 
Mineralogically, sapphire is the name given to all corundum 
gems except the red variety, ruby. Popularly, it is the 

Fig. 70 Sapphire Crystals from Ceylon 

[Ward's Natural Science Establishment.] 

name applied to the blue corundum alone. However, the 
stones sold as "Oriental amethyst," "Oriental emerald," 
etc., are really sapphires of the lesser-known but equally 


beautiful colors. The adjective indicates their original 

. "f . 
association with Asia. 

Corundum belongs to the hexagonal system. Its familiar 
shape is the long, doubly tapered crystal, shown in the 
drawing of Fig. 17 and the sapphires of Fig. 70, but most 
crystals of ruby tend to be short and stubby. 


The exotic barbarity of its color has associated ruby 
with the passion of the Orient. Few other gems have been 
called upon to express so much symbolism. Following the 
traditions of the Poles and the Russians, American gem 
dealers have appropriately designated ruby as the birthstone 
for July. Surely its fiery red is like the summer sun. 

The romance of ruby is intimately concerned with the 
story of India, where the stone was probably first worn in 
jewelry. There, on "Mother India's" eastern border, in 
the dependency of Burma, are found the finest rubies in the 
world. The exceedingly rare "pigeon's blood" color deep 
carmine slightly tinged with blue is obtained especially in 
the Mogok Stone Tract and in the near-by Kathe district, 
which are both about one hundred miles north of Manda- 
lay and a lesser distance west of Lashio, the southern ter- 
minus of the Burma Road. 

.Control of the mines was secured in 1597 by the king 
of Burma, who is said to have exchanged a piece of worth- 
less territory for the precious land and thus become "Lord 
of the Rubies." Successive rulers leased the workings to 
licensed miners who paid rent both in money and in stones. 
All gems over a certain size were forfeited to the king, 
and consequently more than one fine stone was broken 


to evade the law. The finding of a larg(y:uby was the 
occasion for a national celebration, and Tne stone was 
escorted from the mine to the throne by a guard of uni- 
formed soldiers. About sixty years ago the mines were 
leased by a French company, but upon the annexation of 
Upper Burma by the British an English firm was granted 
the concession, and Burma Ruby Mines, Ltd., was formed, 
which marketed its product in London. 

Native methods of recovering the ruby are quite primi- 
tive. A shaft is sunk to the gem-bearing earth, which 
is hauled to the surface in baskets; the rubies are separated 
by washing, then sorted and graded. Different systems 
are used in the wet and the dry seasons. Large investments 
for machinery were made by the British, but the loss of 
money was so great that hand methods were restored. The 
production varied from year to year, sometimes one or 
two large rubies accounting for almost the entire output. 
Formal operation of the Burmese mines ceased long before 
the war and the Japanese seizure of the area, but the local 
inhabitants continued to work the deposits in simple fashion 
until they were flooded and bombed. 

Ruby of a paler color is found with sapphire in the gem 
gravels of Ceylon. A district in Siam known as The Hills 
of Precious Stones has been an important source of darker 
ruby since early days. In both places sapphires far out- 
number rubies, however. Other less important sources are 
Indo-China, Rhodesia, and Afghanistan. 

Because corundum of every color except red is called 
sapphire, the gradual transition from ruby to pink sap- 
phire makes the naming of a light-red specimen a matter 
of individual interpretation. Both the red of ruby and 
the green of emerald are believed to be due to an oxide 


of chromium, the chemical having a different structure in 
each of the two gems. A strange phenomenon is that ruby 
will turn green if heated to a high temperature and will 
retain its new color until almost cool again. Presumably, 
when exposed to heat, the chromium temporarily takes 
on the state that it normally has in emerald. Iron oxide 
may contribute to the color of ruby, and radium radiation 
may possibly assist in producing the finest hue. The color, 
which varies from rose to purplish, holds well under arti- 
ficial light; the best aspect may be obtained by careful 
cutting of the rough stone. 

Some ruby when cut with a rounded top displays a six- 
rayed star across the surface, like that shown by star sap- 
phire, but star rubies are much rarer. 

The word ruby comes from the Latin rnber meaning 
"red" and at one time was used to indicate every stone of 
that color. Even today the term is sometimes misappropri- 
ated and red garnet is sold by such deceptive names as 
"Cape ruby" and "Arizona ruby." 


Esteemed greatly by the ancients, sapphire even today 
has lost none of its appeal to lovers of beauty. Mirroring 
the serenity of an autumn sky, blue sapphire is a perfect 
choice for September's birthstone. The other colors of 
the gem, furthermore, are of a seemingly endless variety, 
although as yet the blues are the only ones that are well 

The original meaning of the word is uncertain; it per- 
haps had an astrologic connotation. It is usually given as 
"blue," which accurately describes the opaque blue stone 


(speckled with gold) which we call lapis lazuli, and we 
are now confident that this was the sapphire of olden times. 
However, the true sapphire became known by the time of 
the New Testament and was probably the stone called 
jacinth in Revelation. 

. There are a number of famous sapphires with interest- 
ing stories. One of the finest rough stones is the Rospoli 
sapphire, a perfect crystal found in India by a native spoon- 
maker. In the British Museum there is an image of Buddha 
carved from a single stone. Until several years ago the 
largest sapphire ever known was among the lost treasures 
of an Oriental king; but even it has been surpassed by the 
Gem of the Jungle. This tremendous stone was found 
when a bolt of lightning uprooted a tree which had con- 
cealed it. Weighing 958 carats in the rough, it was bought 
by an American dealer for over $100,000 and cut into 
9 stones, the largest of which weighed more than 66 

The most valuable sapphire is a rich, velvety, corn- 
flower or royal blue. Montana sapphires are an appealing 
"electric blue" found in no other gem. Orange, yellow, 
green, and purple sapphires are also wonderfully beauti- 
ful. Pink sapphire merges into true ruby. The odd name 
padparadschah refers to a golden-red variety, more often 
seen, however, in synthetics than in nature. 

Star sapphire has been among the most popular of gem- 
stones during recent years. When cut with a rounded 
top it exhibits a six-rayed star across its surface. This fea- 
ture is due to a peculiar crystal structure which reflects 
the light in such a way that a complete star is formed. 
The star is an inherent part of the stone, so that a gem 
may be cut into any number of smaller ones, yet if prop- 


erly oriented each will contain a whole star. The wearer 
of such a stone has indeed a unique gem. Fortunately, 
many of the less expensive colors show the clearest stars. 
An approach to transparency is much to be desired, but 
complete transparency is impossible in a star stone. 

The Orient is the home of the sapphire. Siam yields at 
least half (and much the better half) of the world's supply, 
chiefly from an area on the Gulf of Siam extending some- 
what into Indo-China. India furnishes most of the larger 
stones; during a brief but spectacular career in the late 
19th century the province of Kashmir produced the most 
glorious sapphires ever seen. Emphasis should be placed 
on the many superb sapphires, including the star variety, 
that come from the island of Ceylon. Neighboring Burma 
is also an important but little-appreciated source. Aus- 
tralia (although its stones are dark) and Montana are other 
significant sources. In fact, sapphires from Fergus County, 
Montana, mined by a British firm and shipped for cutting 
to Europe, were the result of the most intensive gem- 
mining project ever carried on in the United States. The 
need for bearings for war instruments was primarily re- 
sponsible for the recent revival of the Montana industry, 
although some gem material has also been obtained. 


Spinel occupies a curious position in the world of gems. 
The genuine stone is hardly known under its own name, 
since it resembles ruby and sapphire, occurs with them in 
the same deposits, and is often confused with them in sell- 
ing. The synthetic spinel, also, is usually called by some 


other name according to its particular color, and many a 
pretty ring is set with a synthetic spinel instead of the gem 
that it is supposed to contain. 

Several magnificent gems which had been thought for 
centuries to be rubies have been proved recently to be 
spinels. One of these, known as the Black Prince's ruby, 
is the large oval stone in the front of the British Imperial 
State Crown. It was given to the Black Prince by Pedro 
the Cruel in the 14th century, and was later worn by 
Henry V on the helmet which saved his life at the battle 
of Agincourt. Another superb red spinel among the Brit- 
ish crown jewels is the Tribute of the World. It is the 
largest in existence. Changing owners as a result of suc- 
cessive conquests over a period of 500 years, it was finally 
presented to Queen Victoria after the Indian wars, but its 
identity was made known only from the ancient Persian 
inscriptions engraved upon it. 

Spinel is hard and durable, well suited to the most in- 
tensive wear. It crystallizes in the isometric system in 
sharp octahedrons resembling two pyramids joined base 
to base (Fig. 71), or in twinned crystals placed side by 
side. It has a variable chemical composition and is regarded 
either as an aluminate of magnesium or as a multiple oxide 
of magnesium and aluminum. The magnesium may be 
replaced by a considerable amount of ferrous iron or man- 
ganese, and the aluminum by ferric iron or chromium. 
Most gem spinel, however, is essentially pure, although 
some blue stones do contain a small percentage of zinc. 

The colors of spinel span the rainbow. Red stones re- 
semble ruby and are colored by the same chemical, 
chromium oxide. Rubicelle is the orange-red variety; such 


a choice-quality flame spinel brings a high price. The 
familiar term "balas ruby," applied to the pink and rose- 
colored spinel, is of course a misnomer. Blue spinel has 
an interesting steely color and is rare. Almandine spinel 

^ ; /f^ 

Fig. 71 Octahedral Crystals of Spinel from Orange County, 

New York 
[From Hawkins The Book of Minerals, copyright 1935.1 

has the purplish-red color of the true almandite (which, 
however, is a garnet). Several of the spinel varieties are 
not transparent but show good colors. These include the 
green chlorospmel (containing ferric iron), the brownish 
picotite (containing chromium), and the almost-black cey- 
lomte or pleonaste (containing ferrous iron). 

Spinel has always been found with the corundum gems 
in Burma, Siam, and Ceylon, which are still the chief pro- 


ducing localities. Far a thousand years good stones came 
from metamorphic deposits in Afghanistan visited by 
Marco Polo. . 


The varieties of the species chrysoberyl are so strangely 
unlike one another in appearance that merely looking at 
them gives one little indication of their close relationship. 
But the scientist, with ingenuity and perseverance, finds 
that the differences between them are rather superficial, 
and that their fundamental characteristics are much the 
same. Lovers of the beautiful and the romantic find chry- 
soberyl to be among the most fascinating of gems, both for 
its appeal to the eye and for its intriguing story. 

THfe name, meaning "golden beryl," indicates the orig- 
inal idea of the identity of this stone, but it is now known 
to have no connection with beryl except that both con- 
tain the rare clement beryllium and the common element 
aluminum. Chrysoberyl is classed either as a multiple oxide 
of beryllium and aluminum or as an aluminate of beryllium. 
Other chemicals (iron and chromium) present as a replace- 
ment are responsible for the interesting colors. Unless 
twinned, as shown in Fig. 2, the crystals of chrysoberyl 
are rather ordinary looking (Fig. 22), sometimes having 
six sides, although they belong to the orthorhombic and 
not the hexagonal system. Very important is the great 
hardness, which is exceeded by only two other minerals, 
diamond and corundum. 

Here is a pair of jeweler's tweezers. Let us pick up 
these stones, one at a time, and learn why they have for 
so long thrilled gem connoisseurs. 



Alexandrite has been called "an emerald by day, an ame- 
thyst by night." It is green when viewed in daylight but 
turns raspberry or columbine red under artificial light, the 
change being due to different color absorption which var- 
ies according to the kind of illumination. Alexandrite was 
discovered in Russia a century ago on the day that the 
future czar Alexander II became of age and was named 
after him. Oddly enough, its twin colors were those of 
the Imperial Guard, and for a time the stone was not found 
outside Russia. 

Ceylon is the source of most present-day alexandrite, 
which is mined there from placer deposits. Fine stones 
are rare and give promise of becoming even scarcer. The 
artificial stones represented as alexandrite are either glass, 
synthetic corundum, or synthetic spinel, and are described 
in Chapter 7. (There are no true synthetic alexandrites 
having the same composition and properties as the natural 
gem.) The synthetics are more bluish in daylight and lack 
the rich hues and dramatic color changes which make a 
fine alexandrite one of the most appealing of Nature's 


No greater contrast to an alexandrite could be imagined 
than a cat's-eye, with its mysterious band of light which 
glides across the rounded surface of the gem as it is moved 
from side to side, exactly like the eye of a living cat. Cat's- 
eye has long been held in high esteem by the Moors and 
the Hindus, who believe that it protects wealth and even 


causes it to increase in value. Natives of Ceylon consider 
it a charm against evil spirits. British royalty has favored 
the gem for engagement rings. 

The shifting light of cat's-eye is called chatoyancy. It 
is caused by reflection of light from great numbers of 
very small hollow canals, as many as 65,000 to the inch, 
arranged parallel to the main axis of the crystal. To show 
the effect to best advantage, the gem must be cut with a 
curved top, similar in shape to a coffee bean, with the 
canals running across the width of the surface; the "pupil'* 
of the eye then appears down the length of the stone at 
right angles to these canals. The narrower and sharper 
the line, the better the gem is considered to be. 

Apple green, honey yellow, and dark green are the most 
highly prized background colors of cat's-eye. Variously 
contrasting bands add to their beauty. In the Maryborough 
collection was a splendid gem carved into a lion's-head 
cameo, with shifting shades of light that gave an amazingly 
lifelike appearance. Another magnificent cat's-eye was 
among the crown jewels of the king of Kandy and was 
later placed in the Hope collection. It is so cut that the 
natural markings in the stone resemble an altar lighted by 
a torch. 

Cywophme (meaning "wave of light") is a name ap- 
plied by some gemologists to those cat's-eyes which, instead 
of a sharply defined streak, show a hazy floating light. The 
same names, however, are frequently used interchange- 
ably for both kinds. 

Most of the world's supply of cat's-eye comes from 
Ceylon, the "jewel case of the Orient." Brazil is another 


A variety of quartz, somewhat similar in appearance to 
the chrysoberyl gem, is called cat's-eye by many persons, 
but it lacks the rich beauty of the chrysoberyl variety and 
brings only a moderate price. This quartz cat's-eye and a 
closely related stone called tiger's-eye are discussed among 
the gems of the silica group in Chapter 5. 

Countless thousands of "Chinese cat's-eyes" were sent 
home from South Pacific islands during the war, or were 
set in rings, bracelets, and pins that were made by hand on 
the spot. These attractive "stones" are really the lids of 
snail (gastropod) shells, and of course have no kinship with 
any mineral cat's-eye. Such a calcareous plate, with a 
dome-shaped top and the luster of porcelain, comes in 
various colors and is called an operculwn. 

Other Chrysoberyls 

Another variety of chrysoberyl is unlike those already 
mentioned. It has no such unusual optical properties but 
is a transparent, usually pale, yellowish-green gem with a 
pleasing luster. Its name is chrysolite chrysoberyl, the 
word chrysolite being derived from the Greek meaning 
"golden stone." The leading sources are Brazil, Ceylon, 
and Rhodesia. 

. Chrysoberyl occurs also in lovely clear greens, yellows, 
and browns which make attractive, though little-known, 
gems. Excellent lemon-yellow stones come from Brazil; 
light-green ones, also from that country, seem to have a 
promising future. Bright colorless crystals have recently 
been found in the Gold Coast in Africa and in the ruby 
mines of Burma. 



The radiant flash of rainbow colors that is the essence 
of diamond is surpassed three-fold by that of the well- 
known mineral but little-appreciated gem, sphalerite. In- 
asmuch as its dispersion is 300 per cent greater, the spectra 
. are three times as wide as those in diamond. Their inten- 
sity, however, is weakened by the diluting effect of the 
yellowish-brown body color of the gem against which 
they appear. Such an amazing characteristic, nevertheless, 
combined with a bright (though tending toward resinous) 
luster and a fine brilliancy, raises the question as to why 
sphalerite is not used more often in jewelry. Cut speci- 
mens are sought eagerly for collections, but the physical 
properties seriously violate the requirements for a jewelry 
stone. Sphalerite is entirely too soft, and its sensitive six- 
way cleavage makes it difficult to cut and susceptible to 
easy breakage. 

The very scarcity of transparent material would prevent 
sphalerite from becoming familiar enough to create its own 
demand rarity is not always a virtue. Except some from 
Mexico and Spain, little sphalerite of gem quality has been 

In its common brown-to-black form, however, sphaler- 
ite is a widespread mineral. Composed of zinc sulfide, it 
supplies most of the world's zinc. Miners call the ore 
"rosin jack" (in allusion to the luster) or "blackjack," and 
the British refer even to the gem as zinc blende or blende. 
The crystals belong to the isometric system and are inter- 
esting because they have almost the same atomic pattern 
as diamond (Fig. 1 ) and were the first to be studied with 



Though rarely met with in jewelry, cassiterite possesses 
all the attributes of a first-rate gem except hardness. Its 
optical characters rank close to the top third in brilliancy 
and second in both color dispersion and birefringence. It 
is, incidentally, the heaviest of all the gems, surpassing even 
the opaque metallic stones in specific gravity. 

Cassiterite, however, is valued chiefly for its content of 
tin. It is almost the only commercial source of the metal 
and is frequently called tin-stone. Its origin is in deposits 
formed by heated gases. Owing to its hardness, lack of 
cleavage, and resistance to chemical action, cassiterite is 
often concentrated in placers. 

The localities in the Federated Malay States and the 
near-by Dutch islands of Sumatra, Banka, and Billiton have 
been brought to public attention by the war. Bolivia is the 
other main source of supply. The British deposits in Corn- 
wall have been famous for 2,000 years. Australia, Mexico, 
East Africa, and central Europe are additional producers. 

Crystals of cassiterite (Fig. 15) belong to the tetragonal 
system. They are sometimes twinned in an interesting 
knee shape. When sufficiently transparent for fashioning 
into gems, cassiterite is astonishingly beautiful. Combined 
with a diamondlike luster, the other optical properties pro- 
vide rich overtones for the deep-golden color of the gem. 


The mineral fluorite formerly held its place in gem- 
ology as a compact violet and purple material called blue- 
John, much in demand for vases and other carved orna- 


mental objects. Exhaustion of the noted deposits at Derby- 
shire in England turned attention to the beautiful faceted 
gems that can be cut from transparent fluorite. They may 
be almost any single color or in several multicolored com- 
binations. Green and yellow tints are often considered 
.the choicest. Rich green gems recently found in South- 
West Africa bear a reasonable resemblance to emerald. 
Attractive pink crystals come from Switzerland. Ontario, 
Canada, produces colorless ones. The United States is a 
major source of fluorite lovely sea-green stones from the 
eastern deposits and purple stones from the extensive Ken- 
tucky-Illinois area and from Colorado. 

Fluorite is composed of two chemical elements, calcium 
and fluorine. It may be referred to as a fluoride, or as a 
halide because fluorine belongs to the halogen group of 
elements, which also includes chlorine, bromine, and iodine. 
The root of its name, meaning "to flow," was originally 
applied to more than one fusible mineral, and was given 
also to the new element when the latter was discovered. 
The spectacular phenomenon of fluorescence, described in 
Chapter 8, was named because of the presence of this prop- 
erty in fluorite, although it is really the result of impuri- 
ties in the stone. The massive material is popularly called 

Fluorite belongs to the isometric system. Although it 
usually crystallizes in cubes, well shown in Fig. 72, its 
cleavage is octahedral and is so well developed that (with 
care) a perfect 8-sided octahedron can be broken from 
a typical 6-faced cube. Twinned crystals, grown to- 
gether so that they penetrate each other, are common. Its 
easy cleavage and conspicuous lack of hardness make 
fluorite a difficult gem to cut or to wear. 


In addition to furnishing specimens for faceting and 
carving, fluorite has a further gem use in the manufacture 
of imitation opal. Industrially, the common variety has 

Fig. 72 Group of Cubic Fluorite Crystals 

[Ward's Natural Science Establishment.] 

great value as a flux in steel-making and as the source of 
hydrofluoric acid. 


For the first time since the discovery of benitoite in 
1907 an entirely new mineral species, not merely a new 
variety of a species already known, has been added to the 
ranks of the gems. Both the mineral and the gem were 
described from the same specimens in 1945 by Frederick 
H. Pough and Edward P. Henderson, who named them 


brazilianite in honor of the country in which they were 

Brazilianite has a pleasing chartreuse-yellow color, like 
some chrysoberyl, and is transparent. Chemically, it is a 
hydrous phosphate of sodium and aluminum, more closely 
resembling turquoise in composition than other minerals, 
but physically it is a very different sort of material. Be- 
longing to the monoclinic system, brazilianite has already 
been found in large crystals; and, although it is by no 
means abundant, it should become sufficiently accessible 
to gem lovers who appreciate its novelty as well as its 
beauty. Unfortunately, brazilianite is neither hard nor 
brilliant and must depend upon its color for any popular 

The best crystals and largest faceted gems may be seen 
in the American Museum of Natural History in New York 
and in the United States National Museum in Washington. 
They were taken from a pegmatite in a part of the state of 
Minas Geraes, Brazil, that is noted for its mica deposits. 


Although it is a fairly common mineral in many rocks, 
and crystals as large as several feet in length have been 
found, apatite is known only occasionally in gem quality. 
Its name bears no relation to food or digestion, but comes 
from the Greek word meaning "deceit"; there is a con- 
fusing similarity in appearance between apatite and other 
minerals because its varied colors resemble those of more- 
familiar gems. Some of these hues deserve wider recogni- 
tion in themselves, however, for the pastel tints are truly 
lovely. Asparagus-stone is the popular and appropriate 


name for the yellowish-green variety. Yellow apatite from 
Mexico has become better known in recent years. Violet, 
pink, blue, bluish-green, and green colors come from other 
countries. Maine, with its violet stones, is the chief Ameri- 
can source. 

Apatite is doubly refractive, as are all gems that crystal- 
lize in the hexagonal system, but hardly any other gem 
possesses the property of birefringence to a weaker degree. 
This has no practical effect on its beauty but is useful in 
identifying the stone on a refractometer. The inferior 
hardness of apatite is its really serious liability. It is the 
standard for number 5 in Mohs' scale and can be scratched 
even by a knife; hence it does not belong in a ring but is 
suitable for other types of jewelry. 

Not only is apatite the most abundant mineral phos- 
phate, deriving its essential element from widespread ani- 
mal and plant remains, but it in turn furnishes the material 
for secondary phosphate gems such as turquoise. 


Best known in jewelry as pink moonstone, scapolite of 
gem quality is more common, however, in transparent 
pieces of other colors that make lovely faceted stones. 
These are rich golden in hue or decline to pale yellow and 
colorless. Faintly clouded specimens of pink, deep violet, 
and blue make most attractive moonstone and cat's-eye 

The first gems were found in the ruby mines of Burma. 
Madagascar and Brazil supply most of the fine yellow 
stones, but those from South America seem at present to 


be off the market. Colorless crystals are a product of the 
volcanic eruptions of Mount Vesuvius. 

Scapolite designates a series of aluminum silicate min- 
erals, in chemical composition very much like the feldspars 
with the addition of chloride, carbonate, and sulfatc mem- 
bers. To make possible an easier classification the series 
has been divided arbitrarily into five parts which have 
been given specific names (the most familiar of which 
is rwernerite}, but they actually grade into one another. 
Scapolite belongs to the tetragonal system and has typical 
four-sided crystals of moderate hardness. 


So intense is the dichroism of cordierite that the twin 
colors of the different rays of light passing through the 
gem can be seen without the aid of an instrument deep 
blue when viewed down the length of the crystal, and pale 
blue or pale yellow when viewed across the width. Other 
commonly used but discredited names for this gem are 
"dichroite" (from its most characteristic property) and 
"iolite." "Water sapphire" is an improper name still used 
among the older jewelry firms and in Ceylon, the chief 

Cordierite is about as hard and as heavy as quartz and, 
except for the extreme dichroism, resembles it in appear- 
ance; some of the violet stones, which look like amethyst, 
especially resemble quartz. Although cordierite belongs 
to the orthorhombic system, twinning causes many crys- 
tals to appear hexagonal; most of the gem material, how- 
ever, occurs in rounded pebbles. Cordierite is a complex 
silicate of aluminum, iron, and magnesium. Its trans- 


parency and hardness place it appropriately with the 
faceted gems, although specimens seem to be cut more 
often as cabochons. 


Associated with diamond in the great mines of Kimber- 
ley are found several other gems of much less value but 
considerable interest. Perhaps the most beautiful of them 
is green enstatite. Having small orthorhombic prisms, the 
crystals furnish bright, transparent gems which would 
have a wider appeal if they were more numerous. 

In spite of being called "green garnet," enstatite is in no 
way related to demantoid or any other garnet. It is a 
member of the important pyroxene group of minerals, 
which includes such gems as diopside, jadeite jade, and 
spodumene. Enstatite is a silicate of magnesium; it usually 
contains a variable amount of iron and may contain some 
aluminum. Iron and chromium together produce the best 
green color. 

Although enstatite possesses only a moderate degree of 
hardness, its extreme resistance to heat and acids suggested 
its name, which is derived from the Greek word meaning 
"opponent." Besides South Africa, Burma also yields gem 
material. Meteorites, which are mineralogically similar to 
kimberlite, the diamond-bearing rock, furnish enstatite for 
the connoisseur. 

As the amount of iron increases, enstatite darkens and 
grades first into bronzite and then next (at 15 per cent 
ferrous oxide) into hypersthenethe end member of 
this enstatite series of orthorhombic pyroxenes. Both of 
these minerals yield gems of a rather metallic appearance; 


they are cut with rounded instead of faceted surfaces. 
Bronzite has a fibrous bronzy luster. Hypersthene exhibits 
a peculiar iridescence called schiller, caused by reflections 
from tiny brown scales of an unknown mineral enclosed 
within it. 


Attractive transparent gems of a bottle-green color are 
furnished by the mineral diopside. They resemble peridot 
but are less olive in shade. Diopside occurs in monoclinic 
crystals showing a good prism form and many faces. Its 
name comes from the Greek and means "double appear- 
ance" in reference to the property of double refraction, as 
a result of which each ray of light is split into two rays 
upon entering the stone (see Fig. 42). 

Diopside is a silicate of calcium and magnesium belong- 
ing to the pyroxene group of minerals. The green color is 
due to iron; when chromium is present it gives a brighter 
tone. The hardness is fairly low for a gem. 

Piedmont, Italy, supplies the most beautiful stones. From 
the Tirol province of Austria, the diamond mines of South 
Africa, and deposits on both the New York and Ontario 
sides of the St. Lawrence River come other fine gems. 
Brazil, Madagascar, and Ceylon are reported as recent 
sources. A fibrous cat's-eye variety comes from Burma. 

The association of diopside with jadeite and feldspar is 
especially interesting in many of the "jade" objects of 
early man that have been found in Mexico and Central 
America, such as those shown in Figs. 88 and 89. 

Violane is an Italian variety of diopside named for its 
excellent violet-blue color; because it is not transparent, 
it is cut as cabochons rather than faceted. 



It is a long way from the world's largest crystal 90 
tons of spodumene, 47 feet long, lying like a huge timber 
in the Etta Mine near Keystone, South Dakota to the ex- 

Fig. 73 Kunzite Crystals from Madagascar 

[Ward's Natural Science Establishment.] 

qiiisitely fragile gems of the same species which grace our 
dainty jewelry. Until the discovery in Brazil about 1870 
of a transparent yellow variety suitable for gem purposes, 
spodumene was known only as an ordinary mineral, fairly 
common in pegmatites, from which it had been abstracted 
for use as the chief source of lithium, the lightest of all 


Since then, choice green and beautiful lilac gem varieties 
have also been found, and spodumene is now properly 
ranked with the significant gem minerals. The two special 
varieties just mentioned have their own names, hiddenite 
and kunzite; in gemology the name spodumene itself is 
generally applied only to the occasional bright yellow or 
yellowish-green gems from Brazil and Madagascar. 

Spodumene another of the pyroxene group of minerals 
is a silicate of lithium and aluminum. Its monoclinic 
crystals (Fig. 73) are dominantly prismatic, marked par- 
allel to their length by alternating grooves and ridges. 


The emerald-green variety of spodumene called hid- 
denite has been found only in one place, in Alexander 
County, North Carolina. Because of the descriptive origin 
of so many gem names, it might be guessed that this stone 
was named because its limited deposit was long concealed. 
It was actually named, however, in honor of William E. 
Hidden, who discovered in 1880 the original deposit from 
which some loose crystals had previously come, though 
their true composition was not learned until later. Gem 
lovers regret that no more new specimens of hiddenite are 


Fascinating color changes make kunzite one of the love- 
liest of gems. It is perhaps the most difficult gem to cut 
because of the extreme perfection of the cleavage, but, 
when properly fashioned to take advantage of its extraor- 


dinary dichroism, kunzite rewards us with gleams of lilac 
and pink exclusively its own. It was first found in 1902 
at Pala, San Diego County, California, and named for 
George F. Kunz, Tiffany's gem expert. It has since been 
found in Connecticut, Maine, North Carolina, Brazil, and 
Madagascar (Fig, 73). 


The story of bcnitoite is like a familiar chapter in 
astronomy in which a new star or planet is known to exist 
long before any observer can fairly claim to have seen it. 
In the identification of benitoite, the tale is even more 
involved. Before a single specimen was found, its crystal 
form was determined theoretically, and mathematics proved 
that such a rare class of crystals is possible in nature. When 
finally brought to light in 1907, it was not even recognized 
but was mistaken for sapphire. Only the curiosity of a 
California jeweler, Godfrey Eacret, led to further inquiry. 
He held a piece in front of a dichroscope and became 
doubtful of its identity when he saw twin colors of blue 
and white a different combination from that which he 
expected. His suspicion was fully justified by the final 
disclosure that this rich blue stone of true sapphire color 
was not only a new gem but a completely new species of 
mineral, until then unknown to science. It was named in 
honor of San Benito County in which it was found. A 
wonderful group of crystals from this unique locality is 
shown in Fig. 74. 

Not only does benitoite have such a strong dichroism 
that the separate colors are visible without an instrument, 


but the dispersion or fire is similarly remarkable, equalling 
diamond in strength. The spread of rainbow colors is less 
conspicuous in benitoite than in diamond, however, be- 
cause it is masked by the bright blue of the gem itself. 

Fig. 74 Large Benitoite Crystals from San Benito County, 

[Ward's Natural Science Establishment.] 

Chemically, benitoite is a silicate of barium and titanium. 
Associated with it was another scarce titanium mineral 
called neptunite, previously found only in Greenland. In 
addition to the disadvantage of its rarity, benitoite is a little 
softer than the minute quartz particles that are ever present 
in the air. 


The largest benitoite crystal weighs less than 8 carats 
and the others are considerably smaller. In fact, the larg- 
est cut stone in private ownership weighs only about one 


Among the fairest flowers of the gem universe is tour- 
maline. Its popularity grows yearly while gem collectors 
and jewelers vie with each other to obtain the finest speci- 
mens for their respective purposes. And with reason for 
tourmaline is one of the wonders of the mineral kingdom, 
presenting an incomparable diversity of color, a complex 
crystal form, a remarkable range of physical properties, a 
curious history. That it was known to the ancients is 
shown by references in their writings to certain of its dis- 
tinctive characteristics; but its exact nature was not under- 
stood and it was thoroughly confused with other gems, 
and its individuality was lost during the unscientific ages 
that followed. In the middle of the 17th century some 
long crystals of a dark-green color reached Europe from 
Brazil and were called "Brazilian emerald," a name which 
has since been applied commonly (though of course incor- 
rectly) to all green tourmaline. 

One summer day in 1703, in the city of Amsterdam, the 
story was further complicated. Several children were 
playing in a courtyard with some colored stones which 
had been brought, together with other foreign merchan- 
dise, from distant Ceylon, then a Dutch possession. The 
hot sun shone down unmercifully, and under its influence 
the stones lost their passiveness and began to attract and 
repel light objects such as ashes and straws. The per- 
plexed traders were unable to account for this startling 


evidence of animation, and disposed of the matter by nam- 
ing the strange playthings ascbentrekkers or "ash-drawers." 
The story spread abroad and the French Academy of 
Sciences was presented with a demonstration of the min- 
eral's inexplicable powers. 

For a period of about forty years serious investigation 
ceased, but interest was suddenly revived when a German 
physician published the results of his private research on 
the subject. Philosophers throughout Europe joined with 
physicists in discussing the mystery, and fashionable so- 
ciety listened with eager curiosity. Specimens were rare 
a Dr. Heberden had the only one in England so that it 
was not until other crystals could be obtained that their 
similarity to certain black stones which had been known 
for many years was discovered. For them all the name 
tourmaline, derived from an old Singhalese word, was 
adopted. Each color variety has its own name, a relic of 
the time when their common relationship was unsuspected. 

The major part of American tourmaline has been found 
in the two most widely separated states, Maine and Cali- 
fornia, as though Nature wanted to grace both shores of 
the continent with the gem which, above all others, reflects 
the ever-varying hues of sea and land. Indians and cow- 
boys collected tourmaline in California as early as 1872, 
and the deposits in San Diego and Riverside Counties were 
perhaps the choicest in the world, especially notable for the 
size and the perfection of their crystals. Pink stones have 
been shipped rather extensively to China (the trade amount- 
ing to $100,000 in the peak year), where many of the stones 
have been cut and resold as finished gems or ornaments. 

Tourmaline was discovered in the State of Maine quite 
by accident. One day at the close of autumn in 1820 two 


students, Elijah Hamlin and Ezekiel Holmes, stopped on 
the summit of a grassy knoll to admire the sunset, when 
one of them was attracted by a flash of green light which 
caught the corner of his eye. Turning to the place he saw 
a broken piece of a green mineral crystal lying among the 
earthy roots of a tree upturned by the wind. Search for 
additional specimens was prevented by approaching dark- 
ness, and plans were laid for the next day. But during the 
night winter came with a heavy snow which covered the 
ground until spring. On the first clear day of the following 
year the two young men resumed their explorations, and 
from cavities in the rock weakened by the elements they 
brought to view some beautiful crystals clear, bright, 
richly colored, delicately formed. They were the first 
of the splendid tourmalines which were to astound gem 
collectors during the following decades. From there- 
Mount Mica in the town of Paris and from Hebron and 
Auburn within close range, have come some thousands of 
excellent stones. 

A few tourmalines have been found in other states also, 
especially Connecticut. They occur in many countries 
but only a limited number are important producers. Bra- 
zilian stones are widely known and admired and constitute 
a leading mineral resource of that nation. Superb gems 
have come from Russia and Siberia. Elba, the island to 
which Napoleon was exiled after Leipzig, has yielded a 
variety of colors. Madagascar tourmalines are equal in 
beauty to those found in more accessible places, and Burma, 
Ceylon, India, and Africa are additional sources of good- 
quality material. 

Color this one word describes the tremendous appeal 
which tourmaline has for the discriminating lover of gems. 


Color in single hues and in polychrome, color exquisitely 
blended and sharply contrasted, color richly streaked and 
delicately modulated, color usually serene, sometimes 
glowing, often shy and furtive evanescent tints which 
come into view and as quickly disappear or merge into 
others. For tourmaline is characterized by a pronounced 
dichroism, so strong that the individual components of 
the color may be seen without an instrument as the gem 
is turned. John Ruskin says whimsically in Ethics of the 
Dusty "All the light that gets into it, I believe, comes out a 
good deal the worse, and is not itself again for a long 
while." Expert cutting endeavors to obtain the most 
favorable color from each crystal. 

Tourmaline varies from water-clear and colorless to 
opaque and black and includes practically every known 
shade and tint of the spectrum's hues. A single crystal 
may be half-red and half-green, crowned with white, with 
lines of demarcation so sharp that the parts seem to have 
been cemented together. Or a "niggerhead" from Elba 
may be colorless for its entire length except a black top; 
or a prism from Madagascar may have a whole row of 
different colors along its edge. Rare specimens have blue 
and green at extreme ends. Many crystals are zoned in the 
opposite way, so that a piece cut as a loaf of bread is sliced 
shows a somewhat circular center of one color surrounded 
by rings of other colors. Brazilian stones often have a red 
core encircled by a white zone and a green outer border, 
resembling a round slice of watermelon. Many California 
crystals are similar but have the succession of colors re- 
versed. This color arrangement of tourmaline is perhaps 
the most remarkable feature of a mineral replete with 


Rose and pink tourmaline is called rubellite. Fine gems 
command a high price, particularly those approaching ruby 
in depth of color. "Brazilian sapphire" is blue tourmaline, 
and indicolite is a deeper blue. "Brazilian emerald" is green 
tourmaline, which is relatively widespread in Brazil; a few 
gems from South Africa are a color that rivals emerald 
and are distinguished from it partly by their superior bril- 
liancy. "Ceylonese peridot" is honey-yellow tourmaline, 
and "Brazilian peridot" is yellowish-green tourmaline. Of 
the other varieties, siberite is violet, dravite is brown, and 
schorl is black; colorless tourmaline is called achroite. As 
mentioned before, these colors occur in almost any com- 
bination, so that tourmaline has earned for itself the so- 
briquet, "the rainbow gem." Tourmaline cafs-eye is suffi- 
ciently fibrous to show a wavy band of light when the 
stone is cut with a rounded top. 

Crystals of tourmaline are unique among minerals. They 
are the only ones that occur in prisms having a rounded 
triangular outline, and they are always lined and furrowed 
along their length. See Figs. 19, 75, and 76. When the 
crystals have faces developed at both terminations, the 
forms at the two ends are different. This phenomenon is 
known as polarity and is made evident in various other 
ways. When a crystal of tourmaline is either heated or 
cooled it is electrically charged, positive at one end and 
negative at the opposite, attracting and repelling small 
particles, as was noticed by the Dutch children two and 
one-half centuries ago. 

The chemical composition of tourmaline is extremely 
complex. To quote Ruskin again, in answer to Mary's 
question, "And what is it made of? "-"A little of every- 


75 Group of Tourmaline Crystals 
from New York 

[Elmer B. Rowley.] 

Fig. 76 Gem Tourmaline Crystal from Brazil 

[Ward's Natural Science Establishment.] 

thing; there's always flint, and clay, and magnesia in it; 
and the black is iron, according to its fancy; and there's 
boracic acid, if you know what it is; and if you don't, I 
cannot tell you today, and it doesn't vsignify; and there's 
potash and soda; and, on the whole, the chemistry of it is 
more like a medieval doctor's prescription than the making 
of a respectable mineral." The different kinds of tour- 
maline really belong to a mineral series. The beautiful 
tints are due mostly to the presence of alkalies. Rubellite 
owes its lovely red to lithium and, associated with the 
lithium mica, lepidolite, forms attractive museum speci- 
mens. Brown tourmaline contains magnesium, and the 
black stones are, as Ruskin said, colored by iron. 

Tourmaline is suitable for all types of jewelry, but its 
moderate hardness and its wealth of pleasing color render it 
especially desirable for costuming. Black tourmaline has 
had a limited vogue as a mourning stone. Besides its orna- 
mental uses, for which its color is responsible, tourmaline 
has a number of scientific applications that are dvie to its 
peculiar electrical properties. It measures the intensity of 
radium emanations; in "tourmaline tongs" it serves to 
detect polarization; small variations in pressure, such as 
those experienced by submarines, are registered by it; and 
it is valued for experimental work in electricity. During 
the war a scientific agency of the British government (lo- 
cated in Washington) advertised for tourmaline crystals 
half an inch or more in diameter. 

Because of its exceptional color characteristics and its 
intriguing story, tourmaline has been successfully featured 
by many jewelers, who have used it to create a new 
fashion among the gem-loving American public. Collec- 


tors of beautiful things display their pieces of tourmaline 
with justifiable pride. 


Beryl is a mineral species comprising several gem va- 
rieties the names of which are more familiar than its own. 
The only gems, in fact, sold simply as beryl are those of a 
pale green color. The rest have distinctive popular names 
emerald, aquamarine, morganite, heliodor, and goshenite. 
The first two, emerald and aquamarine, deserve special 
attention, for they are among the choicest precious stones. 

The mineral beryl is a silicate of aluminum and beryl- 
lium (a chemical element named for it). Small amounts 
of other elements replace these and are responsible for 
the individual colors that so glorify the jeweler's window. 
Without coloring matter, irregular masses of beryl are 
white; many of them probably are mistaken every day for 
common quartz. Crystallized beryl without coloring mat- 
ter is clear and transparent, hardly different in appearance 
from glass except for its hexagonal outline; occasionally it 
is called goshenite. 

Crystals of beryl have a characteristic shape, prisms with 
six sides. Usually the ends are flat, though sometimes they 
are modified by small faces which give a tapering effect, 
as shown in Fig. 18. Huge crystals of beryl, weighing 
hundreds of pounds but of no use for gem purposes, occur 
in some deposits. Such specimens (and smaller ones as 
well) have acquired a vital place in modern industry, be- 
cause the metal beryllium taken from them makes a copper 
alloy which has a tensile strength far greater than that of 


any known steel and can be made into springs that will 
actually flex billions of times before wearing out. 


Of all the gems that might have been chosen as the 
birthstone for May, none could be more appropriate than 
emerald, "green as a meadow in spring." A fine emerald, 
completely transparent and of an intense velvety color will 
bring a truly astonishing price; such a stone may well be 
called the rarest of gems. 

Deficient in brilliancy and fire, even somewhat in dura- 
bility, emerald depends for its popularity entirely upon 
its unsurpassed color. (Chromium oxide is the coloring 
agent.) Freedom from flaws is much less important than 
color unless the structure is quite poor; flaws, in fact, are 
often reproduced in imitation emeralds. 

The first emeralds came from mines known to Alexander 
the Great. These deposits were rediscovered in the Egyp- 
tian desert near the Red Sea by an expedition sent out in 
1818 to search for the ancient diggings which had been 
lost for so long that their existence seemed mythical. Cleo- 
patra was one of the best customers of these mines and 
gave many of the stones to her favorite ambassadors. 
Caesar collected emeralds, presumably for their supposed 
curative value. Specimens have been found in mummy 
wrappings, in Etruscan tombs, and in the ruins excavated 
at Pompeii and Herculaneum. Charlemagne's crown and 
the famous Iron Cross of Lombardy were both set with 
emeralds. When Henry II was made king of Ireland in 
1171 he is said to have been given an emerald ring as sym- 


bol of his authority; if the story is true, this is a pertinent 
association between the gem and the Emerald Isle. 

The Crusaders and Marco Polo returned from the Orient 
with emeralds among their treasures. But these excited 
little interest compared with the amazement expressed 
when the Conquistadores returned to Spain with vast 
quantities of emeralds of a larger size and a more beauti- 
ful color than had ever been seen before. These "Spanish" 
or "Peruvian" emeralds, which actually had come from 
Colombia, were seized from their owners, the Incas, who 
worshiped some of them and guarded them in sacred 
temples. Preferring the destruction of their beloved green 
gems to their theft, the priests told the conquerors that 
real emeralds could not be broken, and a goodly number 
of stones were thus sacrificed in attempts to prove their 
genuineness. Deliberately hidden from white men, some 
of the mines were later found accidentally; others may yet 
remain undisclosed. The densely jungled elevations of 
Colombia still produce the world's finest emeralds, so 
gently described by O. O. Mclntyre as "like wet grass 
in the shadow of great trees after a summer rain." Muzo, 
Chivor, and Coscuez have furnished most of the crystals 
for several decades. For various reasons, some economic 
but others political and rather fantastic, these mines have 
been worked only sporadically. 

So characteristic is the parallel, steplike pattern of cut- 
ting that is used for this gem that the name emerald cut has 
been given to it. Many expensive diamonds also are fash- 
ioned in emerald cut; conversely some emeralds are cut in 
the usual brilliant style of diamond. 

Emerald is more easily fractured than the other varieties 


of beryl and is slightly (though not to any important ex- 
tent) less hard than the rest. 

Very recently emerald has been added to the limited 
number of gems made synthetically on a commercial basis. 
Other man-made substitutes for emerald are either solid 
glass or composite stones assembled from two or three 
pieces of various materials. All of these are explained in 
Chapter 7. 

In addition to the gems from Colombia, choice small 
emeralds have come from the Siberian side of the Ural 
Mountains. Brazil, the Tirol, the Transvaal, and North 
Carolina are other sources, but they seldom figure in the 


The pleasant name aquamarine comes from the Latin 
words for "sea water," so descriptive of its color, a lovely 
blend of blue and green, varying like the color of the sea 
itself. Most of the stones are greenish blue to bluish green, 
one hue or the other predominating, though some are pure 
blue. Occasionally yellowish-green beryl has been called 
aquamarine, but the newer name of chrysolite aquamarine 
seems preferable. Iron oxide is the coloring agent in all 

'Aquamarine's popularity during recent years is a con- 
tinuation from the time when it was the only gem regu- 
larly faceted by the Romans, who valued it for eardrops 
and unengraved ring stones. It was one of the favorite 
engraving stones of European Renaissance artists. From 
it the people of India have cut long cylindrical beads to be 
strung on elephant hair. Flattering to blonde and brunette 


alike, aquamarine harmonizes with fabric of every color, 
and it is one of the few stones which retains its full beauty 
under artificial light. 

Since ancient times aquamarine has symbolized happi- 
ness and everlasting youth, perhaps because of its purity 

Fig. 77 Mount Antero, Colorado 

Noted source of aquamarine, and the highest gem locality (14,245 
feet) in North America. [H. L. Standley.] 

of color and the remarkable absence of flaws in its struc- 
ture. Stories have been told that some persons who wear 
aquamarine rings are able to forecast the weather by the 
changing tint of the stone; but this feature, however in- 
teresting, seems to have no scientific foundation. 

Aquamarine is one of the many gems found in pegma- 
tites. Brazil, the most prolific of all the gem-producing 
nations, long has been the chief source of aquamarine 
crystals, some of which are very large. Deep-blue stones 


have recently reached inflationary prices, along with the 
prosperous expansion of the entire Brazilian lapidary in- 
dustry, owing to the termination of exports of cut stones 
from Germany. The bare and hilly state of Minas Geraes 
is the main producing district of most of the kinds of gems, 
and most of the cutting is done in three towns. 

Siberia, Ceylon, and Madagascar are other leading pro- 
ducers. Not many American aquamarines reach the market 
at present, but California, Maine, Connecticut, and North 
Carolina have supplied more than a few choice gems. The 
highest mineral locality in North America is an aquamarine 
deposit on the rugged slopes of Mount Antero, Colorado, 
at an altitude of over 14,000 feet. Fig. 77 is a view of this 
great mountain 


The financial encouragement given by J. Pierpont 
Morgan to the study and the collecting of gems caused 
the pink and rose variety of beryl, first produced in 1902, 
to be named in his honor. The Morgan collection in the 
American Museum of Natural History in New York is 
one of the best in the world. 

Colored by the element lithium, morganite varies from 
pale pink to salmon to a rich rose red. It occurs with 
other pink minerals. The gem-laden island of Madagascar 
in the Indian Ocean off the east coast of Africa is the main 
source of the most beautiful morganite. Deposits in San 
Diego County, California, have yielded numerous crystals 
of a less desirable salmon hue. Brazilian morganite is 
generally pale. 



Yellow beryl has been known in Ceylon for centuries, 
but the discovery in South-West Africa in 1910 of a mag- 
nificent golden stone of the same species aroused a new 
interest in beryl of this color. It was named heliodor, 
meaning "gift of the sun.'' In addition to the iron oxide 
that causes the color of regular yellow beryl, heliodor con- 
tains a radioactive substance that intensifies its splendor. 
Besides Africa, good localities for heliodor and yellow 
beryl are Ceylon and the Soviet Union, and especially the 
Brazilian state of Minas Geraes. 


First found at Danbury in Connecticut, danburite is 
the only gem species other than benitoite to bear the name 
of an American mineral locality. Danburite is related to 
topaz in chemical composition and crystal form, and it 
resembles yellow topaz in color. Madagascar produces 
deep-yellow gemmy danburite; other stones descending 
through various degrees of yellow to completely colorless 
ones are said to come from there and also from Burma 
and Japan. 

Danburite is a silicate of boron and calcium. Its ortho- 
rhombic crystals have much the same prismatic shape as 
topaz but are not handicapped by the latter's fragile cleav- 
age. A luster of more than average brightness, a good 
refractive power and consequently an adequate bril- 
liancy when cut, and a hardness equal to quartz make 
danburite a worth-while gem mineral. 



When Job praised the value of wisdom and said, "The 
topaz of Ethiopia shall not equal it," he referred to a 
stone which we know today as peridot, the gem variety of 
the mineral olivine. Its source was an ancient mystery, as 
the older name may indicate, since the word topaz may 
perhaps be derived from the name of the island Topazios 
in the Red Sea where the gem was obtained. According 
to the story, the place was thus named because it was so 
hidden by fogs that mariners had difficulty in locating it. 
This triangle-shaped island, now called Zeberged or St. 
John's, is 34 miles off the coast of Egypt. Pirates are said 
to have been the first to land there and to have discovered 
the stones in crevices in the rock. Knowledge of the place 
was later lost to the outside world for centuries. Almost 
the entire supply of peridot has come from this one lo- 
cality. Many fine stones were brought to Europe by the 
Crusaders who thought them emeralds, and a large num- 
ber of the peridots sold today have been recut from these 
historic gems. The new supply is limited; some crystals 
that appeared in the American market not long ago were 
purchased avidly. 

At its finest, peridot has a rich bottle-green shade dif- 
ferent from any other gem. So lovely is this stone that it 
often has been called "evening emerald." A more modern 
description comes from a French journalist: "Peridot is 
primeval green, green as a signal light." Its name fre- 
quently is pronounced in the original French way, to 
rhyme with "go," as well as in the Anglicized way to 
rhyme with "got." 


Olivine received its name from its typical olive-green 
color and its olive-oil luster. Chrysolite, meaning "golden 
stone," is the attractive name properly given by jewelers 
to the variety of olivine that has a yellow or greenish- 
yellow color, but this term is so generally misused in ref- 
erence to other gems that are blends of green and yellow 
that it has almost lost its individuality. Furthermore, 
chrysolite is the recently adopted name for the group of 
minerals to which the species olivine and the olivine series 

No gem could have a more amazing career than the 
olivine found in meteorites strange celestial visitors, the 
only things from outside his own Earth that man is able to 
see and touch and analyze. Peridot of a size and quality 
actually suitable for use in jewelry is a constituent of the 
solid part of some of these "shooting stars." 

In addition to the Egyptian island already mentioned as 
the chief source of peridot, other places from which gem 
material comes are the diamond mines of South Africa, 
and localities in Ceylon, Brazil, Burma, Australia, and the 
United States. In the Navajo land of Arizona and New 
Mexico large rounded pebbles of peridot have been eroded 
from the primary rock to find their way into ant hills and 
sand dunes. 

Chemically, olivine is a silicate of magnesium and iron, 
which replace each other in varying proportions. In hard- 
ness it is inferior to the majority of the well-known gems 
and thus is better adapted to pins and necklaces than rings. 
Crystals of olivine, though often much abraded, usually 
show the stubby prism of the orthorhombic system to 
which they belong (see Fig. 21). 



More phenakite has been found than the scarcity of cut 
gems might indicate. Owing to the interesting forms dis- 
played by the hexagonal crystals, most of them are doubt- 
less left in their original state without being fashioned. 

The name (formerly also spelled "phenacite") is de- 
rived from the Greek word meaning "deceiver" because 
of the frequency with which the crystals have been 
mistaken for quartz. The superior optical properties of 
phenakite, however, make identification certain when in- 
struments are used. 

Phenakite is usually colorless but may be light brown, 
bright yellow, or rose. Some phenakite is very trans- 
parent and, although somewhat lacking in fire, has an 
exceptionally appealing luster. 

A silicate of the rare element beryllium, phenakite oc- 
curs with other gems, especially beryl, that are chemically 
related. Mount Antero, Colorado, is the most important 
locality in North America. Here aquamarine, the gem 
variety of beryl, has been partly dissolved, furnishing 
beryllium for the subsequent growth of the phenakite. 
Beautiful large crystals have come from the emerald mines 
of the Ural Mountains, a gold mine in Brazil, and Tan- 
ganyika Territory in East Africa. 


Occasional clear slender prisms of willemite, of a deli- 
cate apple-green color, and a few transparent light-yellow 
pieces as well, have been cut into gems. Willemite be- 
longs to the hexagonal system of crystallization. It is 


fairly heavy but not very hard. Its most startling prop- 
erty is a bright fluorescence, described in Chapter 8. Only 
from the great zinc mines of the Franklin-Sterling Hill 
district of Sussex County, New Jersey, has come gem- 
quality material, though ordinary willemite is found in a 
few other places. 

Willemite is a silicate of zinc, constituting in New Jersey 
an important ore of that metal. Intensified production 
during the war diverted to industrial use many specimens 
that might otherwise have gone into collections. The 
Franklin area is noted for its tremendous variety of min- 
erals, many of which do not occur anywhere else in the 
world. Willemite is intimately associated with franklinite 
and zincite, the three minerals together forming handsome 
multicolored specimens. 


Garnet represents more than merely a single mineral 
having several color varieties. It is really a group of min- 
erals, comprising half a dozen subspecies, five of which 
have gem varieties of their own. The chemical formula is 
uniform in type for all the garnets, and the constituent 
elements are interchangeable when their atoms are ap- 
proximately equal in size, though the total valence or com- 
bining power must be maintained. This ability of atoms 
or ions to replace one another, called isomorphism, explains 
the range in composition and the variation in properties. 
Some kinds of garnet, however, like some cousins among 
the human race, do not mix as freely as others; and even 
among the more hybrid garnets there is usually a sharp 
enough distinction to enable a proper classification to be 


made. Gem garnets especially may be properly classified 
since, like all gems, they are more exclusive, more restricted 
in their range, than common minerals. 

Few other gems are as widely sold as garnet, but few are 
so misunderstood. Garnet has been sold under a host of 

Fig. 78 Garnet Crystal in Pegmatite from Pennsylvania 

[From Hawkins The Book of Minerals, copyright 1935.] 

false names, though even the correct names are confusing, 
particularly to those persons who, familiar only with the 
reddish-brown stones, do not know that garnet occurs 
in almost every color except blue. Many of the lesser- 
known garnets are certainly attractive and some are highly 

Garnet crystals (Figs. 12 and 78) may be easily recog- 
nized by their distinctive shape, usually having cither 12 or 
24 faces, each 4- or 6-sided, unless they are worn by the 


processes of nature to nearly round pebbles. Although 
most of them are small, some attain fairly large sizes; one 
crystal weighing over nine pounds was found in 1885 in an 
excavation just off Broadway in New York City. Lacking 
cleavage, garnet is not easily broken. Because of its high 
refractive index it is very brilliant when properly cut. 

Ordinary garnet, of no gem value, is used as an indus- 
trial abrasive for polishing wood and leather. During the 
war a nonskid, fireproof, plastic material containing par- 
ticles of garnet went into service on battleship decks to 
prevent accidents caused by slipping. 

Synthetic garnet is not made commercially; on the con- 
trary, the real stone is substituted for more expensive ones 
in composite man-made gems to give them a hard outer 

Modern research has shown the existence within the 
garnet group of two natural isomorphous series, each 
named for the subspecies that constitutes its middle mem- 
ber. Onecalled the almandite series embraces pyrope, 
almandite, and spessartite. The otherthe andradite series 
includes grossularite, andradite, and uvarovite. Each of 
these subspecies except uvarovite (which yields no gems) 
is described in this section. 


Pyrope, the best-known garnet used in jewelry, is a sili- 
cate of magnesium and aluminum. Its name is derived 
from the Greek word meaning u fiery," because of its 
sparklike color, red with a yellowish cast. 

Properly known as Bohemian garnet from its former 
chief place of origin, this stone is frequently sold as a 


variety of ruby under such fraudulent names as "Cape 
ruby/' "Arizona ruby," and "Colorado ruby." In each 
instance the adjective discloses the source. 

A virtual flood of pyrope garnets came from Bohemia 
in the 19th century. They were mounted in pins and 
brooches of unattractive Victorian design, and their abun- 
dance gave them (and all garnets) an unpleasant reputa- 
tion among women of fashion. Even the discovery of 
really beautiful pyrope in the diamond mines of South 
Africa failed to restore its popularity, and misleading names 
were adopted for merchandising purposes. Pyrope is 
found in lesser amounts in other countries besides those 
mentioned, and in Colorado, Arizona, New Mexico, and 
Utah in the United States. 


The exquisite color of roses and rhododendrons is pre- 
served forever in the rare rhodolite garnet. In composition 
it stands between pyrope and almandite, consisting of two 
parts of the former mineral to one part of the latter. 
Except a discovery made in Greenland during the war and 
identified in 1946, rhodolite has been found only in Macon 
County in western North Carolina, where it was first re- 
ported in 1893. Most of the crystals are tiny, and conse- 
quently the cut gems are even smaller, but their lovely 
color is a delight to any eye fortunate enough to see them. 


As the magnesium is replaced by ferric iron, pyrope 
grades imperceptibly into almandite. Roman gem engrav- 


ers were fond of this garnet, known popularly as alinati- 
d'me but preferably as almandite, and from it they carved 
some superb cameos and intaglios. The Head of the Dog 
Sirius in the Marlborough collection is considered the 
finest intaglio ever created. A portrait of Plato engraved 
in almandite is the most familiar likeness of him. 

At its best this garnet has a deep, clear red color, usually 
tinged with violet. It is highly prized in India, where the 
wealthy classes call it precious garnet and wear it with 
their diamonds and rubies. Almandite is the gem known 
for 2,000 years as carbuncle, and it has often been cut with 
a rounded top. This style of cutting (cabocbon} is itself 
at times wrongly called carbuncle, but the latter word 
should be applied only to a red garnet so fashioned. The 
mineralogical spelling almandite is a scientific approach to 
uniform terminology. 

That amazing optical instrument, the spectroscope (Fig. 
47), which reveals the intimate secrets of chemistry, shows 
a typical iron absorption spectrum in almandite, especially 
in the violet stones. 

Almandite gems come from the prolific deposits of 
Ceylon, from India, from Brazil and Uruguay in South 
America, and from a few other countries. Stones suitable 
for jewelry are found in about a dozen states of the United 
States but are hardly numerous. The large garnet crystal 
previously mentioned which was uncovered in New York 
City was almandite. The interesting crystals from Alaska 
have almost no value as gems. Almandite is the garnet 
most widely used as an abrasive; some commercial de- 
posits, such as the one near Lake George, New York, 
also contain gem material. 



One of the prettiest of the garnets is unfortunately too 
rare, and usually too small, to attract much notice. Spes- 
sartite, the manganese-aluminum garnet, is usually red of a 
golden or brownish hue. The mineral is fairly common in 
Maine and elsewhere in the United States, but gem-quality 
material comes from only a few localities. Tiny perfect 
crystals are found in cavities in three volcanic hills at 
Nathrop, Colorado. A number of good stones have come 
from northern Brazil. Other scattered sources include 
Ceylon, Burma, and Australia. The locality of Spessart 
in Bavaria gave its name to the subspecies. 


Garnets with a hazy, spotted interior that indicates a 
granular structure belong to the subspecies known as 
grossularite, the calcium-aluminum member of the group. 
Stones the color of gooseberries give the mineral its name, 
from the Latin word for that berry. When they have the 
golden-brown color of cinnamon they are called hessonite 
or cinna?)i on-stone. Even choicer colors are orange, called 
hyacinth-garnet, and reddish brown, called jacinth-garnet. 
Translucent pale-green grossularite was discovered a few 
years ago in the Transvaal and is sold as "South African 
jade" which it would probably resemble, if there were any 
jade in South Africa! A pink variety of grossularite in 
snow-white marble is mined in Mexico. The other colors 
come mainly from Ceylon. 



The most remarkable of all the garnets is green. Its 
name is demantoid, which means "diamond-like," and it is 
a variety of the mineral andradite. Here is a gem with a 
flashing luster, a fiery inner brilliancy, and the most ex- 
treme display of rainbow colors shown by any major 
precious stone. Although it may give forth yellowish 
tints, its choicest hue is a true emerald green. Demantoid 
was discovered in the Ural Mountains during the middle 
of the past century. At first it was believed to be emerald 
and was called "Uralian emerald"; now it is sometimes sold 
also as "olivine"; both names are erroneous and are used 
merely because they are supposed to sound more attractive. 
This wonderful rare gem needs no such deception. Inas- 
much as it is found only in small sizes and is not especially 
hard, it is usually limited to being a foil for other, larger 
stones. Many have been set in rows and circles in diamond- 
set rings and sold as emeralds. 

Two other gem varieties of andradite are known. To- 
pazolite, named for its resemblance to yellow topaz, has 
come from Switzerland and Italy. Melanite is black and 
has served in mourning jewelry. 

All three kinds of andradite are calcium-iron garnets 
and are the softest of the entire garnet group. 


The pistachio color of epidote is easily recognized. 
Faceted gems have been cut from transparent crystals of 
this distinctive yellowish-green shade and have often been 


called pistacite. Other clear hues exist, but they are not so 
well known, although opaque green specimens are very 
common in metamorphic rocks. 

Epidote is the general name given to a group of im- 
portant minerals, as well as to a series within the group 
and specifically to the most abundant member. They are 
hydrous silicates of calcium, aluminum, iron, and other 
elements. Another mineral in the group, zoisite, is de- 
scribed in the chapter on "Cabochon and Carved Gems." 
Epidote itself is monoclinic, and its crystals are often hand- 
some, having a prismatic aspect and exhibiting many faces. 
Gem material has come from Austria, Italy, and Norway. 


Zircon is no longer the gem of mystery. Until the last 
ten years, however, less had been known about its consti- 
tution than about that of any other precious stone, and its 
history, even the origin of its name, is still obscure. Yet 
zircon is one of the oldest gems; its scientific nature makes 
it one of the most extraordinary. 

Early in the 20th century three kinds of zircon, rather 
than one, were believed to exist. To avoid the confusion 
of giving them separate names, it has been more convenient 
to refer to them as high, low, and intermediate zircon, 
according to the physical and optical properties. 

According to this interpretation high zircon is the fully 
crystallized silicate of the element zirconium. Low zircon 
has no outward crystal form and is apparently a mixture 
of amorphous oxide of silicon and some kind of zirconium 
oxide, which may be partly crystalline. Intermediate zir- 
con is composed of both the normal silicate and the separate 


oxides and fills the gap between the extreme high and low 

The current decade has revealed more intimately the 
physical secrets of zircon and showed that the so-called 

Fig. 79 Zircon Crystals in Matrix 

[Ward's Natural Science Establishment.] 

high zircon is the normal kind and includes most of the 
gem varieties. High zircon belongs to the tetragonal sys- 
tem and occurs in square prisms with pyramids at both 
ends (Figs. 14 and 79). A twin crystal is shown in Fig. 
3. Radioactivity due to the presence of thorium breaks 
down the crystalline structure to an increasing extent 
until, by a gradual transition accompanied by changes in 


specific gravity, refractive index, and other properties, the 
mineral becomes low zircon. The cloudiness characteristic 
of many zircons is evidence of their internal disintegration 
from the normal state. 

With these variations in structure is a similar variation 
in color. Perhaps zircon has no such complete extent of 
hues as is found in corundum or tourmaline. But there is 
enough choice to satisfy most tastes, and some of the colors 
are indeed splendid. The deep-red gems reflect from their 
depths a penetrating glow, and the green stones with their 
peaceful beauty present a fine contrast. The rich golden- 
yellow gems are truly magnificent, surpassing all other 
stones of that color. The lovely blue zircons are de- 
servedly popular, having been named starlite by Dr. Kunz 
because of their resemblance to "stars twinkling in the 
night." By no means least in interest are the colorless 
gems, whose resplendent brilliancy, dazzling luster, and 
concentrated fire make them the nearest rival of diamonds. 
Normal zircon is most likely to range from colorless to 
orange red or blue. Altered zircon may be brown, yellow, 
or green. 

Zircon was better known until recently by the names of 
its varieties, hyacinth and jacinth, which appear in the 
older literature. The word zircon, which may have been 
dejived from an Arabian or Persian word that described 
one of the colors of the stone, was rarely used in the gem 
trade until the introduction of the blue and the colorless 
kinds, but it has now become thoroughly familiar. It has 
largely superseded the names starlite for the blue, and 
jargoon or "Matura diamond" for the colorless zircon. 
The word Matura is similar to Matara, the southernmost 


harbor of Ceylon, from where the transparent colorless 
gem was exported. 

Both hyacinth and jacinth are now correctly applied to 
red, orange, yellow, and brown zircons of gem quality, 
although if a distinction is made, hyacinth may be the 
reddish brown and jacinth the more nearly pure orange in 
color. Surely the best improvement would be to call all 
of them zircon, with suitable adjectives to indicate the 

Ancient artists found zircon a responsive medium for 
their skill. Greek gem carvers specialized in intaglios, in 
which the design was incised below the surface; the Ro- 
mans engraved both intaglios and cameos, most of the 
latter being in the darker stones. These classic specimens 
are characterized by roundness of line and shallowness of 
figure to avoid cracking the gem. Renaissance artists 
worked much with pale-yellow zircon, but produced 
cameos slightly inferior to the best of earlier periods. 

The feature of zircon marketing that has attracted the 
greatest interest is the artificial production of certain colors. 
When the starlite blue, the golden-yellow, and the color- 
less diamondlike varieties began to acquire extensive popu- 
larity in America after the First World War, considerable 
discussion was aroused about their occurrence in nature. 
Some of them have indeed been found, but only rarely, 
and a profitable industry was built up at that time in the 
creation of these desirable colors. The Oriental process 
that is used has become generally known only since 1936. 
Between 850 and 1,000 degrees centigrade the reddish- 
brown stones from Indo-China usually turn golden yellow 
or colorless when heated in air, and blue or colorless when 


heated in the absence of air. Nothing dishonest is in- 
volved in this method of changing the color; the other 
properties remain about the same, and the chief effect is 
to give us gems that are admittedly more beautiful. 

Most of the heat treating, as well as the cutting, is done 
across the border from Indo-China at Bangkok, the capital 
of Siam; the location of the industry explains the mistaken 
references to "Siamese zircons." Japanese conquest put 
a temporary end to outside purchases of zircon originat- 
ing in Indo-China, but the brown, yellow, and green gems 
from Ceylon continued to be available. 

The gem district of Ceylon lies between Kandy, the 
capital, and the south shore near Ratnapura, which means 
"City of Gems" in Singhalese. In this interesting oriental 
island, known to the Chinese as the "Isle of Gems," is the 
greatest concentration of precious stones in the world, the 
deposits furnishing every important species with the single 
exception of diamond. The stones are scattered through- 
out a layer of gravel called illaw, which lies under a thick 
bed of clay. Above the clay is fertile ground cultivated 
for centuries as rice fields. The work is done by natives 
who receive three-fifths of the proceeds. A pit is dug and 
the earth is hauled to the surface in baskets; then it is 
washed in a stream, and the stones are separated from the 
mud. They are sorted into groups according to size and 
quality. Many crystals have been worn into irregularly 
rounded pebbles by the sorting action of running water, 
which, together with tropical conditions of weathering, 
aggregates the gems into placer deposits. 

Some fine zircon has been taken from places outside the 
Orient. Yellowish-red stones come from Russia, and red 


gems of good color have been found in New South Wales. 
The diamond-bearing rock at Kimberley in South Africa 
carries a quantity of yellowish-brown crystals of zircon, 
which are called by the miners "Dutch bort," a disreputable 
epithet justified by their lack of value. Zircon occurs at 
several localities in the United States, but material suitable 
for fashioning into gems is rarely encountered. The clear 
and brilliant crystals from the Pikes Peak region of Colo- 
rado are unfortunately too small. 

That zircon has other remarkable qualities besides color 
to make it a most worth-while citizen of the gem kingdom 
is evident from a brief mention of its physical properties. 
A happy combination of an adamantine luster, a high re- 
fractive index, and a dispersion only 14 per cent lower 
than that of diamond makes a fine colorless zircon re- 
semble a diamond so closely that in direct sunlight or under 
bright artificial illumination not many persons can easily 
discriminate between them. 

Zircon is not characterized by excessive hardness and 
is peculiarly subject to chipping around its edges; yet if 
given the careful treatment due all rare and valuable things, 
zircon will reward its owner with long and faithful service, 
giving constantly what it most possessesbeauty. 

The specific gravity is higher than that of any other 
major nonmetallic gemstone, so that a zircon is smaller in 
diameter than a diamond of the same weight. 

In the history of chemistry zircon is noted for having 
furnished to science two rather rare elements. Zirconium 
was discovered in the mineral in 1789 and named after it, 
and the most closely related element, hafnium, was first 
detected in a Norwegian zircon in 1922. 



Datolite leads a double life. European writers refer to 
the pale-green and yellow gems cut from transparent 
crystals of complex forms. Americans, on the other hand, 
are better acquainted with the light-colored, often mottled, 
opaque masses resembling unglazed porcelain which are 
found with inclusions of native copper in the Lake Superior 
copper district of Michigan. The facet-cut type is the 
more valuable because it is rarer and more difficult to cut, 
and therefore deserves primary consideration. 

Datolite is a silicate of boron and calcium, which 
crystallizes in the monoclinic system and has an inferior 
degree of hardness. Its curious crystals are found in the 
United States in New Jersey, Massachusetts, and Connec- 
ticut, and in central Kuropc, especially Austria. 

Very similar in chemical composition to danburitc, 
which is sometimes found with it, datolite is closely re- 
lated in a structural way to euclase (which may be said 
to belong to the datolite fwuily). None of these three 
gems has more than a limited use. 


Like aquamarine, euclase is a gem containing the ele- 
ment beryllium (as a hydrous silicate of beryllium and 
aluminum), and also, like aquamarine, it comes in deli- 
cately lovely tints of blue and green. The chief reason, 
apart from a certain rarity, why stones cut from euclase 
are infrequently seen is their very perfect cleavage, which 
makes cutting difficult. The name of the mineral, in fact, 
means "good cleavage." Its resistance to scratching is 


almost equal to that of aquamarine. Euclase occurs in 
prismatic crystals of the monoclinic system. Gem-quality 
stones come from Brazil, the Ural Mountains, India, and 
East Africa. 


Topaz recommends itself to the aesthetic taste by its 
perfect transparency, its velvety luster, its enchanting hues, 
and its softly diffused body appearance. Topaz is indeed 
an appropriate birthstone for November, mirninH the 
golden tone of autumn leaves and the rich glow fldian- 
summer sunsets. Yet all topaz is not yellow, nor are all 
yellow stones topaz, as is widely believed. The colors of 
topaz are many; they are usually of delicate tint; there are 
few dark stones. Red colors are especially scarce, but 
clever applications of heat, called "pinking" and carried 
on mostly in Brazil, turns some brownish topaz to the 
blushing rose and pink hues that have been in vogue during 
recent years. Blue and light-green topaz are indeed lovely. 
Even the colorless stones are appealing, for there is some- 
thing about their shining surface and peculiar slippery feel 
that is quite individual. 

Citrine, the yellow variety of quartz, is the gem most 
often confused with topaz and sold in place of it, but surely 
citrine is inferior in richness and delicacy of color, as well 
as much cheaper in price. Attempts are still being made 
to effect standardization of gem names, particularly citrine 
and topaz. 

The derivation of the word topaz is uncertain. The 
original name was applied to the variety of olivine now 
known as peridot. Conversely, the word chrysolite, an- 
other present-day name for olivine, was once used to in- 


dicate the true topaz. A probable source of the word topaz 
is the Sanskrit tapas, meaning u fire," for some of its colors 
merit such an appellation. 

Topaz is an aluminum silicate containing fluorine and 
water, which indicate an origin through the action of hot 
acid gas. It is found mostly in pegmatites, granitic rocks, 
and in the placer deposits accumulating from their dis- 
integration. Topaz is a frequent associate of tin ore, and 
the presence of either one is a useful indication of the 

Crystals of topaz (Figs. 20 and 80) are distinctive in 
appearance, since they have exceptionally smooth faces, 
sharp edges, and a large base. Topaz has an extremely 
easy cleavage parallel to the base, so that a crystal may 
be split into any number of thin slabs with little trouble. 
This fragility is somewhat offset by great hardness. Among 
precious stones topaz ranks fourth in hardness; hence it 
resists the abrasive effects of ordinary use. 

The relatively common occurrence of topaz in large 
crystals (see Fig. 80) keeps the cost of large cut stones 
low. A piece weighing 1 3 pounds was used as a doorstop 
by a London merchant until its identity was revealed and 
it was removed to the British Museum of Natural History. 
The enormous stone known as the Braganza diamond, 
which is among the treasures of Portugal, is believed to be 
topaz, but for a long time no one competent to form an 
opinion on it has been allowed to examine this 1,680-carat 
gem. Topaz gems of the most fascinating colors may be 
seen in the great mineral collections of our larger cities. 

Brazil produces topaz of a rich yellow-brown color- 
called imperial topaz in that country as well as most of 
the stones that are altered in color. Fancy pink topaz and 


red topaz bring a high price, and blue stones are increasing 
in cost. Ceylon stands high in today's market. Russian 
and Siberian topazes are among the magnificent gems of 

Fig. 80 Huge Crystal of Gem Topaz from Brazil 

[Cranbrook Institute of Science.] 

the world. Other main foreign sources are Burma, Japan, 
Australia, the British Isles, and several of the gem- 
producing countries of Africa. 

In the United States lovely blue topaz formerly came 
from San Diego County, California. Colorless and sherry- 
colored stones are found in the Thomas Mountains of Utah 


and are prized for their sparkle when cut. Splendid 
crystals have come from Colorado's mineral deposits; per- 
haps the largest complete topaz crystal ever found in North 
America was taken from Devil's Head in 1935. Several 
other states, especially those of New England, have pro- 
duced topaz of gem quality, and the annual American 
output has on occasions exceeded $5,000. Massive topaz 
without any gem value has recently become an industrial 
mineral mined in ton lots in South Carolina for use in 


So named because of the wedge shape of its crystals 
(Fig. 27), axinite is a rare gem of unusual colors. It pre- 
sents a choice of hues, including honey yellow, olive 
brown, and violet blue, which are accentuated by a strong 
dichroism that lends a charming evanescent effect. The 
luster is particularly pleasing. 

The chemistry of axinite is complex, as the mineral is a 
hydrous silicate of boron and aluminum and contains sev- 
eral other elements substituting for one another. Axinite 
is approximately as hard as quartz. It is the only trans- 
parent gem besides kyanite that belongs to the triclinic 
system, the least symmetrical of the six main kinds of 
crystals. Axinite of the colors mentioned occurs in the 
French Alps, Tasmania, and several American localities. 


In its usual brown or green color, faceted andalusite 
closely resembles tourmaline of the same hue. The green 
gems are most striking when viewed along the main 


crystallographic axis, for their strong dichroism causes 
bright flashes of red to gleam against the contrasting back- 

Another interesting, though much less valuable, variety 
of andalusite is called cbiastolite. It is never faceted, but 
when sections of it are polished they show a black cross 
which is due to the odd arrangement of the carbon matter 
present in the center. Chiastolite should not be confused 
with the completely cross-shaped u fairy stones" of stauro- 
lite, which owe their form to the intergrowth of two 
twinned crystals; both minerals are used in Christian coun- 
tries as amulets. 

Andalusite is an aluminum silicate with the same chemi- 
cal formula as sillimanite and kyanite. Crystals of anda- 
lusite occur in square prisms belonging to the orthorhombic 
system. Transparent andalusite is somewhat harder than 
quartz, whereas chiastolite is considerably softer because 
of the difference of its interior. 

The original source was the southern Spanish province 
of Andalusia, from which the mineral derives its name. 
Ceylon and Brazil furnish most of the current supply. 
Chiastolite comes from Siberia and Australia. The United 
States, particularly Massachusetts, yields both kinds. 


Occasional light-blue and green specimens of sillimanite 
appear in the gem trade. Their lack of distinction lies in 
the fact that they look much like several better-known 
gems of similar pale colors. 

Crystals of sillimanite are long slender prisms of the 
orthorhombic system. Many of the stones are water- 


rounded, so that their original form is no longer evident. 
Sillimanite is slightly superior in hardness to quartz. In 
composition it is an aluminum silicate and has the same 
formula as andalusite and kyanite. Burma and Ceylon 
are the leading sources of gem material. 

Sillimanite was named after Benjamin Silliman, a pio- 
neer American geologist. Another name for it was fibro- 
lite in reference to the typical fibrous structure of some 
of the material. Now, however, the name fibrolite is 
reserved for the fibrous variety only, some of which is 
grayish green or brown, resembling jade, and some of 
which shows a cat's-eye effect owing to the reflections 
from the tiny fibers. 


Alone among all the minerals of the world in its 
variable hardness, kyanite has the curious ability of resist- 
ing the scratch of a knife in any direction except down 
the length of the crystal. This peculiar property is a sure 
means of identification. 

Kyanite is one of few gems having the authentic color 
of blue sapphire. In its lighter blue tints it resembles aqua- 
marine, and it may also be almost colorless; the prevailing 
hue, however, is so typical of kyanite as to suggest its 
name, which means "blue." ("Cyanite" is an obsolete 

An alternative name is disthetie, meaning "double 
strength/' in reference to the unequal hardness in dif- 
ferent directions. The crystals are triclinic, in long blades, 
which usually have a concentration of color in the center, 
surrounded by a white margin. This color contrast is 
augmented by a strong dichroism. 


Kyanite has exactly the same chemical formula as an- 
dalusite and sillimanite, all three being aluminum silicates. 
Because it possesses a very easy cleavage, and its cleavage 
surfaces show a pearly luster, uncut kyanite tends to 
exhibit a characteristic rippled surface unlike the more 
.compact smoothness of other gems. 

India and Burma produce kyanite in gem quality, as do 
Switzerland, Brazil, Kenya in East Africa, and the United 
States. Some beautiful kyanite of an uncommon green 
color comes from North Carolina. 


With a dazzling surface luster and a display of rainbow 
colors excelling even diamond, sphene presents a mag- 
nificent appearance. So high, also, is its refractive index 
that a standard jeweler's refractometer fails to give a read- 
ing. In dispersion or fire sphene surpasses all the major 
gems with the sole exception of andradite garnet. In the 
extent of its double refraction sphene is even more im- 
pressive, standing alone at the top. A dichroscope shows 
marked differences in the hues of the individual rays trans- 
mitted through the darker stones. 

With these astonishing optical properties, and a group 
of distinctive colors as well, sphene merits attention in any 
company of gems. 

The name in Greek means "wedge" and clearly de- 
scribes the odd-shaped monoclinic crystals shown in Fig. 
24. Previously it was generally applied to the lighter 
colors, which are confined to green and yellow, while the 
now-discredited name "titanite" was used to indicate the 
darker, mostly brown, stones. At the present time sphene 


is the accepted name of the species and includes the green, 
yellow, and brown colors, both light and dark. 

As the word titanite suggests, this gem contains the 
chemical element titanium and is a silicate of titanium and 
calcium. The extraordinary optical characteristics of 
sphene are not matched by its other physical properties, 
for the hardness is considerably inferior to that of quartz, 
and the specific gravity is quite modest, almost exactly the 
same, in fact, as diamond, which too is notable for its low 
density as compared with its high refraction. 

Gem sphene has come from Austria, Switzerland, Can- 
ada, and the northeastern part of the United States. 


Chapter 4 

Cabochon and Carved Gems 

The amateur gem cutter of today begins, as did the 
earliest lapidary of ancient times, to work with the softer 
stones, fashioning them into cabochons before attempting 
any facet cutting, which demands a superior degree of 
mechanical skill and mathematical precision. Cabochon 
is defined as a stone cut in convex form, polished but not 
faceted; the term applies also to the style of cutting itself. 
Gems shaped in this manner are said to be cut cabochon, 
or en cabochon in the original French (derived from 

The carving of gems involves an even greater ability 
than faceting does, because of the artistic talent required 
to sculpture figures, carve cameos, engrave intaglios and 
seals, and to create other ornamental forms of beauty and 
objects of usefulness in infinite variety. 

Cabochon and carved gems are appropriately and con- 
veniently discussed together, because in general the same 
stones are selected for both types of cutting. Although 
any gem may, of course, be cut in almost any wayfor 
example, the carved diamond in the Chicago Natural 
History Museum the usual media for cabochons and 


carvings are opaque and translucent stones whose appeal 
lies in their attractive color, curious markings or mottling, 
or distinctive optical effects. These materials, it will be 
noted, do not exceed quartz in hardness. They are de- 
scribed by species in the rest of this chapter, which follows 
(with a few unavoidable exceptions) the order of min- 
erals given in the seventh edition of Dana's System of 
Mineralogy. 1 


Metallic gems are judged by their luster, not by their 
chemical composition. Most gems contain a large per- 
centage of some metal, such as aluminum, iron, or copper, 
but its presence is seldom manifested in the appearance 
of the stone. Among the common minerals a metallic 
luster is so frequent that it is used as the major criterion 
for classification in most schemes of determinative min- 
eralogy; but only two gems, pyrite and hematite, have a 
luster like that of a typical metal. 


The brass-yellow color of pyrite has deceived prospec- 
tors so often that they have given it the name "fool's gold." 
The name pyrite is derived from the Greek and refers to 
the sparks that fly when a specimen is struck. 

Pyrite is a ubiquitous mineral, having been formed under 
every kind of circumstance and in almost every type of 
geologic body all over the world. It is an iron sulfide, 

1 Palache, Berman, and Frondel, Harvard University. Published by 
John Wiley and Sons, Inc., New York. Volume I, 1944. 


used as an ore of iron in only a few places because it 
contains too small a proportion of the metal; however, it 
has been on occasion an important source of sulfur. 

It may be one of the most handsomely crystallized of 

Fig. 81 Handsome Group of Striated Pyrite Crystals 

[Ward's Natural Science Establishment.] 

the isometric minerals, opcurring in a distinctive form 
called the pyritohedron and in cubes that are often striated 
in opposite directions on adjacent faces. (See Fig. 81.) 
As is true of other common minerals, however, it is usually 

One novel way in which pyrite is set in jewelry is in a 
single cluster of small natural crystals. Most cut and 


polished pyrite is sold under the trade name "marcasite." 
Real warcasite, which rarely appears in jewelry, is a very 
similar mineral, which has the same chemical formula but 
crystallizes in the orthorhombic system. 


Although it has been cut in a miscellany of faceted and 
cabochon shapes, even including beads to serve as an un- 
convincing substitute for black pearls, hematite makes its 
most frequent appearance in jewelry as intaglios for men's 
signet rings. For this purpose it is an excellent material; 
the design, usually the head of a warrior, is incised by 
hand below the surrounding polished surface. 

The dark-gray color of such a highly reflecting opaque 
gem belies its true color, which is not seen until the stone 
is scratched or broken. Then the cherry-red hue of the 
mineral powder appears, and the origin of the name hema- 
tite, which comes from the Greek word meaning "blood- 
like," becomes obvious. Usually hematite is red because 
it is already in a finely divided state; only crystals and hard 
masses are gray or black. Common hematite is found in 
numerous forms, such as micaceous, earthy, and fibrous. 

Hematite is of tremendous significance to our industrial 
age, since it is the chief ore of iron in the world's vastest 
iron mines, those of the Lake Superior region. Hematite 
is ferric iron oxide; it crystallizes in the hexagonal system. 
The gemstone from Cumberland, England, has the highest 
reputation. Other sources include the island of Elba and 
the Scandinavian countries of Sweden and Norway. 
Hematite imported into the United States since the war 
has been cut in China. 



Four of the nonmetallic gems that are cut into cabo- 
chons or are carved turquoise, feldspar, lapis lazuli, and 
jade may be regarded as major gems, at least from an 
historical viewpoint. Nevertheless, the others described 
here are also well worthy of study, and some of them are 
pushing rapidly into prominence. 


When stained by the presence of impurities, the mineral 
smithsonite, which is white when pure, takes on various 
attractive colors. The translucent green or bluish-green 
material, sometimes banded (Fig. 82), is the most pleasing 
and has become a fairly well-known gem. 

Smithsonite is a zinc carbonate, the zinc being replaced 
in part by other elements. Like related carbonates, of 
which it is the hardest, smithsonite crystallizes in the hex- 
agonal system, though rarely in visible crystals. Its very 
sensitive cleavage in three directions tends to add a pearly 
luster to the vitreous luster of the unbroken surface. In 
some mines smithsonite is an important ore of zinc and 
represents a surface alteration (often indirectly) from 
sphalerite, the primary zinc sulfide, which is itself a 
gem mineral. 

The stone was named after James Smithson, the English 
chemist who was born in France and established the 
Smithsonian Institution in the United States. It may be 
remarked that this mineral was formerly called "calamine" 
in Great Britain; American "calamine" (now named hemi- 
morphite) is an entirely different zinc mineral. 


Material good enough for jewelry conies from Kelly, 
New Mexico; Laurium, Greece; Santandar, Spain; and 
Tsumeb, South-West Africa. 

Fig. 82 Polished Slab of Banded Smithsonite 

[Ward's Natural Science Establishment.] 


For richness of beauty, the silky banded green of mala- 
chite is unexcelled in the mineral kingdom. Its softness 
prevents its use in rings and other articles of jewelry that 
are subjected to much wear, but its bright opaque color 
makes it eminently suitable for pins, necklaces, and but- 
tons. As a favorite stone of Czarist Russia, malachite was 
extravagantly carved into bowls, table tops, vases, and 
jewel boxes. 


The agatelike banding, superbly shown in Fig. 83, is 
due to slow deposition from solution, for malachite is 
a secondary mineral occurring where copper ores have 
undergone certain processes of weathering that involve the 

Fig. 83 Banded Gem Malachite 

[Ward's Natural Science Establishment.] 

addition of carbonic acid. Malachite is a basic carbonate 
of copper, and like all carbonates it effervesces in acid. 

Malachite crystallizes in the monoclinic system, but it 
seldom appears in sharply defined crystals; it is usually 
seen in massive rounded shapes. Most of the crystals of 
malachite that have been found were once crystals of 
azurite (a gem mineral of similar composition) which have 


altered with a fibrous effect to the more stable compound. 
These pseudomorphs are shown in Fig. 84. 

The name conies from the Greek word for "mallow," 
the leaf of some varieties of that plant resembling malachite 
in color. Concentrically banded malachite of superb gem 

Fig. 84 South African Group of Fibrous Malachite Crystals 
Altered from Azurite 

[Ward's Natural Science Establishment.] 

quality comes from the Belgian Congo; other sources in- 
clude Arizona, South Australia, Rhodesia, South-West 
Africa, and the Ural Mountains. In these and other places 
malachite is a valuable ore of copper. 


Although it occurs with malachite, alters to it, and has 
much the same properties, azurite nevertheless presents as 


striking a contrast in color as can be imagined. Its azure- 
blue color, from which it gets its name, is as brilliant as 
the green of malachite. Although not as abundant as mala- 
chite, azurite also is a widespread and useful ore of copper; 
it is, like malachite, a basic carbonate of copper, but the 
two have slightly different chemical formulas. The mono- 
clinic crystals of azurite are not uncommon, though most 
azurite is massive. Azurite changes slowly to malachite 
(Fig. 84) under normal conditions. When both minerals 
have grown together, the resulting gem is called azitrinalci- 
cbite, which is used more frequently as an ornamental 
stone than azurite alone. 


The color of variscite, usually light green to bluish 
green, resembles some hues of turquoise, and the two 
stones have often been confused. But variscite year by 
year is becoming more conspicuous as a distinct American 
gem with a personality of its own. An observer promptly 
focuses his attention on the handsome polished nodules 
of Utah variscite in mineral cabinets, and cabochons cut 
from such pieces are appearing more often in jewelry. 
The recent phenomenal growth of the variscite industry 
was revealed in 1947 when variscite ranked fourth in value 
among the gems produced in the United States. 

The only large deposits of variscite are in northern Utah, 
although the mineral was found long ago in Saxony and 
named after Variscia, a Roman name for the district. In 
Utah the variscite specimens occur in sedimentary rocks in 
brownish or gray nodules or concretions, in which are 
combined several minerals of similar appearance, as well 


as a great variety of other minerals the whole showing 
intricately veined patterns. Cut pieces of variscite that 
include parts of the matrix are called awatrix, a word con- 
structed from "American matrix." Patriotic pride has also 
attached the superfluous name utahlite to the pure variscite. 
Variscite is a hydrous aluminum phosphate, colored by 
chromium, vanadium, and iron. It crystallizes in the ortho- 
rhombic system but is usually massive. 


The present American vogue for turquoise coincides 
with a marked extension of the world's supply. Even 
the excited search for new deposits, however, has failed to 
meet the greatly increased demand. The gem conse- 
quently has been rising in price even more than the exigen- 
cies of inflation warrant. 

Turquoise has completed another cycle in its long his- 
tory of repeated lapses from and returns to favor. Yet 
with certain races it has always been popular. The old- 
est dated piece of jewelry is said to be an Egyptian brace- 
let set with turquoise, which probably came from the 
ancient mines of the Sinai Peninsula. The highest grade 
of turquoise known has come from deposits near Nishapur 
in the Iranium province of Khorosan; small wonder that 
the Persians have regarded it as their national gem! Tur- 
quoise has long been used throughout the Middle East as 
an amulet to protect horses from falling. In the jewelry 
and ornaments of Tibet turquoise is characteristically as- 
sociated with coral, with which it contrasts nicely in color. 

No peoples, however, have regarded turquoise with as 
much admiration as the Indians of the American South- 


west. They mined it industriously for centuries before 
the coming of the white man, and they struggled against 
their conquerors for possession of the deposits. The 
Navajos in particular treasured the stone more than any 
other article and still trade rugs, jewelry, or ponies for it. 

The great mines near Los Cerillos in New Mexico were 
the largest and most famous in America, but, since the 
exhaustion of these sources, near-by states have in turn 
succeeded to the position of chief producer. Nevada is 
in the lead today and Colorado is a close second; Arizona 
and California also yield valuable gems. 

Turquoise may be blue or green or any blend of these 
two colors. A bright blue, often called robin's-egg blue, 
is regarded as the choicest hue. Some wearers, especially 
Indians, prefer a green color, even though it is much more 
common. Most blue stones have an unfortunate tendency 
to turn greenish with age as they absorb grease and oil or 
lose water. Numerous fraudulent attempts have been 
made to restore the faded color. Certain localities, how- 
ever, are noted for the constant hue of the turquoise taken 
from them. 

The cause of color in turquoise has not been established. 
Chemically, the mineral is a hydrous phosphate of alumi- 
num and copper; iron partly replaces either or both of the 
other metals. Various beliefs have been expressed about 
the proportions of copper and iron needed to give specific 
colors, but analyses do not seem to sustain them. 

Thought previously to be amorphous, turquoise was 
proved to crystallize in the triclinic system by the discov- 
ery in Virginia in 1912 of tiny but actual crystals. Every- 
where else turquoise occurs in irregular veins, crusts, or 
lumps in broken rock that is generally volcanic in origin. 


Thin wisps and small patches of other substances, mostly 
kaolin (a clay mineral) and limonite (an iron mineral), 
traverse almost all specimens. The resulting pattern is 
often attractive and is accepted as a sign of genuineness. 
When these veinlets are conspicuous, the material is sold 
as turquoise-matrix. 

The rather waxy luster of turquoise serves to conceal 
scratches; it is fortunate, as the gem is not especially hard. 

In addition to the places already mentioned, turquoise 
comes from several states of the Commonwealth of Aus- 
tralia and from Turkestan. The latter locality may have 
been responsible for the name of the gem, a French word 
referring cither to Turkestan, the source, or Turkey, the 

Odontolite or "bone turquoise" has often appeared as a 
substitute for true turquoise. This curious gem consists of 
the bones and teeth of animals, fossilized and colored blue 
or green by iron phosphate. Its organic texture reveals 
its origin. The name odontolite comes from two Greek 
words meaning "tooth stone." 


The feldspar minerals constitute a group of similar 
species, closely related in chemical composition, crystal- 
lization, properties, and occurrence. Their scientific im- 
portance far exceeds their value in gemology. Neverthe- 
less, the feldspar gems include several varieties of real 

The significance of the feldspars lies in their abundance, 
in the variability of their composition, and in the com- 
plexity of their crystallization. These factors combine to 


make them extremely valuable as a basis for classifying 

j <j 

rocks. With quartz they make up most of the bedrock 
surface of the earth. Unlike quartz, which is remarkably 
constant in chemical composition, they vary enough to 
serve as a fundamental means of differentiation among 
rocks that contain them. A specimen of feldspar the com- 
position of which is known can be very useful in classify- 
ing the rock from which it came. Elaborate methods have 
been worked out for determining the composition of feld- 
spars by microscopic examination of their crystallization, 
particularly their twinning, and entire books have been 
published on this subject. The name that is applied to a 
given igneous rock depends mainly upon the kind and 
amount of feldspar that is present. 

Feldspar is commonly divided into two main types the 
so-called potash feldspars, including orthoclasc and micro- 
cline, and the plagioclase feldspars, which form a continu- 
ous series within themselves. All are silicates of aluminum, 
having potassium, sodium, and calcium as other major con- 
stituents. Orthoclase belongs to the monoclinic system 
and the rest are triclinic, but there is little difference in the 
shapes of the crystals, which appear in Figs. 23, 26, and 
85. A prominent feature of the triclinic feldspars is their 
multiple twinning. Taking place on a small scale, this 
repeated twinning consists of countless parallel planes 
within the crystal and gives rise to a row of closely spaced 
lines or striations (sometimes visible only with a micro- 
scope) on the surface. When two or more kinds of twins 
are present, the structure may form a network pattern. 
The interference of light reflected from such twin planes 
is a major cause of the unusual optical effects that dis- 
tinguish many of the feldspar gems. The close relation- 


ship between the members of the feldspar group makes it 
possible for most of the gem varieties to occur in more 
than one species, because almost all the feldspar gems owe 
their distinctive characteristics to structural peculiarities, 

Fig. 85 Amazonstone Crystals from near Pikes Peak, Colorado 

[Ward's Natural Science Establishment.] 

and these are seldom restricted to only one species of feld- 

A conspicuous property of feldspar is the presence of 
two pronounced cleavages which are exactly or almost at 
right angles to each other. Feldspar is inferior to quartz 
in hardness; orthoclase is the standard for number 6 on 
Mohs' scale. 

Besides being cut into gems, feldspar is widely used as 
a binder and a glaze in the manufacture of porcelain. Some 


is used in glass-making. When regarded as the mineral 
that by the processes of weathering contributes more than 
any other to the formation of soil, feldspar takes on its full 
stature as a vital substance in the world we know. 

Ortboclase. Occupying the first place among the feld- 
spar gems, moonstone has long been a favorite in fine 
jewelry and is perfectly adapted for beads, necklaces, and 
pins, though not durable enough for rings. Its soft radi- 
ance, like the glow of summer moonlight, has a quiet appeal 
that is never tiring. Moonstone usually appears white and 
rather milky until it is held in a favorable position, when 
a lovely sheen sweeps across its face in a subdued flush of 
light, which is bluer, the choicer the gem. 

This optical effect is known as scbillerizatiou. It results 
from an intimate intergrowth called micro pertbite a com- 
bination of two kinds of feldspar, orthoclase and plagio- 
clase. The orthoclase constitutes most of the material 
and acts as a host for thin layers of albite (a kind of plagio- 
clasc). The presence of these layers tends to induce a 
separation or parting along them, and the reflection of light 
from such surfaces causes the schilleri/ation. The spacing 
of these layers determines the color of the sheen. A moon- 
stone must be oriented properly to reflect light; conse- 
quently it is always cut with a fairly steep, rounded top 
and a base that is parallel to the reflecting layer of albite. 

Beautiful blue moonstone is found in Burma. Most of 
the good gems, however, come from Ceylon, where they 
are found in gravels and swamps, as well as in the original 
rock itself. Madagascar and Tanganyika Territory are 
other sources of moonstone. Switzerland was formerly a 
producing locality. 


Not all moonstones have the composition just men- 
tioned. Some are varieties of albite and some are varieties 
of oligoclase and will be discussed later under those mem- 
bers of the plagioclase series of feldspars. There is also 
a pink moonstone, which is a variety of scapolitc, and a 
moonstone of inferior quality which is a variety of quartz. 
But the true moonstone is feldspar, and most of it consists 
largely of orthoclase. 

Two other varieties of orthoclase, both of them trans- 
parent, are also used as gems.- 

A colorless, virtually pure, orthoclase that appears at its 
best when faceted has come mainly from Switzerland but 
is now quite rare. It was named adnlaria after the Adular 
Mountains, which formerly included the St. Gotthard re- 
gion, the actual source. 

Clear yellow orthoclase has been found in Madagascar 
within recent years. It o\ves its fine color to a small distri- 
bution of ferric iron oxide and makes attractive faceted 
stones. Pure orthoclase, such as adularia, is a silicate of 
potassium and aluminum. 

Microcline. Like orthoclase, microcline is a so-called 
potash or alkali feldspar and has the same chemical formula. 
It crystallizes, however, in the triclinic system; its name 
refers to the small inclination by which the two cleavages 
differ from the right angle that they have in orthoclase, 
which means "straight cleavage." 

Awazonstone (or awazonite) is the only gem variety of 
microcline and is also the only green feldspar. Owing to 
its color, which ranges from bluish green through bright 
green to greenish gray, it resembles jade and is often mis- 
taken for it. The name amazonstone itself is the result of 
an error, for the mineral does not occur near the Amazon 


River, but originally in the Ural Mountains. The one out- 
standing locality for amazonstone is the Pikes Peak region 
of central Colorado. When crystals from there, similar 
to those shown in Fig. 85, were displayed for sale at the 
Centennial Exposition in Philadelphia in 1876, their size 
and quality forced the Russian material off the market. 
Amazonstone also comes from Norway, Madagascar, and 
the state of Virginia. It has been cut into beads and 
other rounded forms. It cannot be carved like jade, how- 
ever, because of its easy cleavages. 

Plagioclase. The term plagioclase covers a completely 
isomorphous series of triclinic feldspar minerals, which 
grade into one another without any break. For con- 
venience mineralogists have divided them arbitrarily into 
six species, which have no significance except that each 
expresses a given range of chemical composition. The 
optical and other physical properties change slowly as the 
composition changes. 

The plagioclases are often called the soda-Hwe feldspars, 
because they run from albite, an aluminum silicate with 
sodium (soda), to anorthite, an aluminum silicate with cal- 
cium (lime). The progressive variation from albite to 
anorthite is not merely a substitution of sodium by calcium 
but is more complex, involving a change in aluminum and 
silicon as well. 

Including the intermediate members of the series, the 
plagioclases are named albite, oligoclase, andesine, labra- 
dorite, bytownite, and anorthite. Each of the end- 
members embraces 10 per cent of the whole, and each of 
the others covers 20 per cent. 

Three of these six plagioclases may be represented among 
the gems. 


Albite. Referred to as a sodic plagioclase or an alkali 
feldspar, according to one's viewpoint, albite generally is 
similar in occurrence to the other alkali feldspars, ortho- 
clasc and microcline. The word albite comes from the 
Latin and means "white," its color. 

A rare variety of albite called peristerite, from Canada 
and Madagascar, shows a play of colors when held in a 
certain position, owing to the interference of light that is 
reflected from twinning surfaces having a restricted orien- 
tation within the stone. Since the orientation varies with 
the composition of the feldspar, this interesting effect is 
not frequently seen in albite. 

Some albite also occurs as moonstone. 

Oligoclase. In addition to a small part of the 'moonstone 
that is used in jewelry, oligoclase furnishes some transpar- 
ent colorless stones that are attractive when faceted. Its 
chief contribution to gemology, however, is the variety 
sunstone, a perfect antithesis to the delicate loveliness of 
moonstone. The golden gleams of red and yellow that 
give sunstone its apt name come from light reflected from 
tiny flakes of hematite (a common iron mineral) dis- 
tributed in a regular manner through the stone. The 
spangles disappear if the stone is heated and reappear only 
if the stone is cooled slowly enough. This gem is also 
known as aventurme feldspar from its resemblance to the 
original aventurine, which was the artificial glass contain- 
ing copper filings and now known as u goldstone." The 
richest sunstone comes from Norway where it is a popular 
gem. Other specimens are found in Siberia and in Modoc 
County, California. 

Labradorite. As far as the feldspars are concerned, the 
iridescent play of colors resulting from the interference 


of light rays reaches a culmination in labradorite. This 
common and abundant mineral, occurring in masses that 
weigh millions of tons, ordinarily gray or white at its best, 
becomes transformed on rare occasions, when the structure 
permits, into a sheet of brilliant hue. Across the gray 
surface sweeps a rush of blue or green, as bright as a pea- 
cock's feather the same optical phenomenon is responsible 
in both instancesor of golden red or yellow. The 
primary cause of this effect is the repeated twinning in 
the mineral, the layers of which lie in the direction of the 
least favorable of the two chief feldspar cleavages. 

Labradorite was named after its discovery nlong the 
coast of Labrador in the 18th century. It is found in 
islands off shore, and in Newfoundland and Quebec, and 
in Russia, but gem material forms only the smallest fraction 
of the rock. Labradorite must be cut with a flat surface 
to show its colors properly. 


Although it will be mentioned as one of the four opaque 
blue minerals that constitute the major part of the rock- 
gem known as lapis lazuli, sodalite in some places is suffi- 
ciently homogeneous to be considered a distinct gem. The 
pleasing color is a deeper blue than that of lapis lazuli and 
somewhat more violet. 

In chemical composition sodalite is a silicate of sodium, 
aluminum, and chlorine, and it crystallizes in the isometric 
system. Localities noted for masses of sodalite are three 
provinces of Canada Ontario, Quebec, and British Co- 
lumbiaand Litchfield, Maine. Crystals have been found 
at Mount Vesuvius and material of colors other than blue 


occurs elsewhere, but only the blue massive sodalite serves 
in jewelry and is carved into ornamental objects. 

Lapis Lazuli 

The "sapphire" of the Bible, lapis lazuli, was the most- 
prized blue gem of ancient times, not only for personal 
adornment but also for ornaments and inlaying. Assyrian 
and Babylonian jewelry and seals of lapis lazuli are in the 
most primitive forms. Chinese lapidaries have long carved 
from it small articles, of which snuff bottles are the most 
interesting. In Europe and America it is cut most often 
into beads and into stones for pins. 

Like other opaque gems, lapis lazuli depends for its popu- 
larity upon its color, which is unrivaled among blue stones. 
It is, however, not merely a rich blue but spangled with 
gold and white, resembling, according to Pliny, the star- 
bedecked night sky. 

Its variegated pattern is due to the fact that lapis lazuli, 
alone among the crystalline gems, is not a single mineral, 
but a rock consisting of an aggregate of several minerals. 
It was formed by the metamorphic action of a magma 
body on impure limestone. The molten rock recrystallized 
the limestone to marble and disseminated through it a 
number of new minerals. Any given specimens therefore 
c'ontain different proportions of these minerals. 

The most important constituents of lapis lazuli are the 
blue minerals, for they are chiefly responsible for its beauty. 
Four of them are known, all members of the feldspathoid 
group, so called because they are produced instead of feld- 
spar in rocks that have abundant alkalies but insufficient 
silica. Hauynite has recently been proved to be the main 


constituent, and the others are lazurite, sodalite, and nose- 
lite. One or more of the four may be present, since they 
are isomorphous and partly replace one another. Chem- 
ically, they are silicates of sodium and aluminum; some 
necessary calcium, chlorine, and sulfur are distributed 
variously among them. They crystallize in the isometric 
system but usually in shapeless masses. Their hardness is 
moderate, but opaque stones do not need to be as hard as 
transparent ones which show scratches easily. 

The golden color is supplied by flecks of pyrite, the 
iron-sulfide mineral known as "fool's gold." Its presence 
proves the genuineness of lapis lazuli, although its popular 
appeal changes with the fashions. 

Another common mineral, calcitc, furnishes the white 
wisps and veins. At least half a dozen other well-known 
minerals have been found in specimens of lapis lazuli. 

The name of the gem, now often shortened simply to 
lapis, was given to it in the Middle Ages, partly from the 
Latin word for "stone" and partly from the Arabic word 
meaning "blue"; its resemblance to our words lazurite and 
azure is obvious. 

Until the past century lapis lazuli was doubly prized, for 
it formed the base of the wonderful blue pigment called 
ultramarine, since produced artificially. 

Marco Polo visited and described the remarkable lapis 
lazuli mines of Badakhshan in Afghanistan in 1271. These 
mines have been worked for 6,000 years; near-by deposits 
also yield ruby and spinel. Good lapis lazuli is found 
near Lake Baikal in Siberia. A paler quality is mined in 
the Chilean Andes. Other sources include Upper Burma 
and San Bernardino County, California. The newest lo- 


cality for good gems is near the top of North Italian Moun- 
tain in central Colorado. 


Translucent light-green prehnite of various hues is occa- 
sionally cut as cabochons. The uncut crystals, which 
belong to the orthorhombic system, are distinctive rounded 
aggregates which furnish an easy clue to the identity of 
the mineral. Another green variety of prehnite occurs in 
a more compact manner resembling jade. Prehnite is a 
hydrous silicate of aluminum and calcium. It was the 
first mineral to be named (in 1783) in honor of a person, 
Colonel von Prehn, who brought specimens from South 
Africa to Europe. Prehnite is found with datolite, also 
a gem mineral, and with zeolites in cavities in volcanic 
rocks, where it has been deposited by solutions after the 
consolidation of the lava. Leading sources are New Jer- 
sey, Connecticut, the Lake Superior region, France, and 

Cblorastrolite is a prehnite-like mineral mixture found 
in Isle Royale National Park, the largest island in Lake 
Superior. It makes attractive cabochons. Exactly a cen- 
tury ago it was recognized as a mixture rather than a single 
mineral, but the name persists. 


Jade stars in a double role. It represents two distinct 
minerals, which in some ways are very different, yet in 
other ways are so much alike that only mineralogists try 
to discriminate between them. Moreover, a number of 


other materials that somewhat resemble them often are 
improperly called jade. 

The true jade minerals are jadeite and nephrite. From 
an artistic and historical standpoint they are best treated 
together, for the term jade, which combines both, has 
great significance. From the view of the scientist, how- 
ever, they should be described separately. Attention will 
first be directed to the similarity between them by a dis- 
cussion of jade as a single substance. 

As such it has always been regarded by the Chinese as 
the noblest of gems. It occupies a place in their art and 
their lore that has no counterpart elsewhere. The history 
of China, its triumphs and disasters, its prosperity and de- 
cline, can be read in the styles of jade carving that have 
gradually developed over the millennia and reflect the 
mood, the thought, and the action of a great civilization. 

In a general way, but with highly important variations, 
the trend has been from crude and simple markings to in- 
volved geometric patterns, then to free-flowing designs 
that expressed religious symbolism, finally to sculptured 
forms, which have become increasingly elaborate in mod- 
ern times. Examples of Chinese jade are treasured in many 
museums and private collections (Figs. 86 and 87). Some 
pieces are so intricately worked that they are almost be- 
yond the comprehension of the Western mind. The col- 
lections in New York and Chicago should be seen by 
everyone fascinated by this material. 

Ancient races of both hemispheres used jade to make 
their axes, knives, and other implements and weapons, 
although this practice was early abandoned in China, ex- 
cept when objects such as bowls and plates could be both 


useful and beautiful. The natives of New Zealand special- 
ized in carving weird human figures in jade, but they too 
used it in numerous other ways, as is proved by their name 

Fig. 86 Jade Figure from the Chang Wen Ti Collection 

Fig. 87 Chinese Carved Jade 

[Chang Wen Ti.] 

for jade, axe-stone. The inhabitants of Central America 
and adjacent countries used thousands of pieces of jade 
for utilitarian and religious purposes. Two fine jade carv- 
ings from Central America are shown in Figs. 88 and 89. 


Fig. 88 Mayan Figure, Honduras 

Fig. 89 Aztec Toad, Mexico 

Native American Jade Carvings 

[Middle American Research Institute.] 

Many jade articles have been recovered among the pre- 
historic lake dwellings in Switzerland. 

With the possible exception of diamond, more books 
have been written about jade than about any other gem. 
The noted 100-chapter "Sung" catalogue of jade in the 
collection of Emperor Kao-tsung, alleged to have been 
published in China in 1 176, may be merely an 18th-century 

The name for jade and the word for precious stone are 
the same in the Chinese language. Our word jade comes 
from the Spanish word for it, piedra de ijada, meaning 
"colic stone," which refers to its supposed value as a cure 
for illness. 

The color of jade runs all the way through the spectrum. 
If chemically pure, jade should be white, but it seldom is. 
Jade may have impurities sufficient to make it blue, yellow, 
or almost any hue. A mottled distribution of color is the 
rule in most specimens. Green is so frequently the color 
of jade that it is sometimes carelessly regarded as the only 
color. Some colors are more typical of jadeite, which 
comes in a wider range, whereas others are more often 
seen in nephrite; it is usually difficult or impossible to dis- 
tinguish between the two kinds by sight, especially with 
very old pieces, known as tomb jade, that have been buried 
in graves and oxidized brown. At its best jade may be 
quite translucent, but it is usually opaque. 

The chief characteristic of jade is its extraordinary 
toughness. In hardness, as measured by the scratch test, 
it never exceeds quartz, but it is so immune to breakage 
that it often resists really violent treatment that would de- 
stroy almost any other mineral substance. This durability 
gives jade the essential quality for which it has been valued 


for many centuries and results from the fact that jade 
consists of a compact aggregate of crystals so intimately 
intergrown that they refuse to be separated. 

A curious property of jade is its resonance, reported in 
the oldest Chinese records known to us. The ability of 
jade to yield melody must surely have added to its vir- 
tues in the hearts of the Chinese. 

The source of both kinds of jade poses some interesting 
problems in geography. Only a part of the rough material 
is found in the original rock; the rest is taken from boulders 
whose place of origin often cannot be traced. Much more 
troublesome has been the difficulty faced by archaeologists 
and ethnologists in their attempts to determine the source 
of widespread articles of jade, especially in Central 
America, Mexico, and central Europe. Complex and im- 
probable trade routes have been assumed in some instances 
to account for this distribution. 

Jadeite. Of the two kinds of jade the more valuable is 
jadeite. It is considerably rarer than nephrite and brings 
a higher price when its identity is known. Emerald-green 
stones colored by chromium are called imperial jade and 
may approach transparency. Mutton-fat jade is also a 
favored color, and others include bright yellow, blood 
red, and mauve. These colors are almost always in streaks 
or patches associated with less choice colors. When jade- 
ite is dark green or virtually black because of its high iron 
content, it is known as chloro?nelamte. 

Jadeite belongs to the pyroxene group of minerals, so 
named because one of them was erroneously thought to 
be a "stranger in the domain of fire" yet some of the 
pyroxenes are the most characteristic constituents of high- 
temperature igneous rocks. Other gem members of the 


group, described elsewhere in this book, include enstatite, 
diopside, and spodumene. Jadeite is a silicate of sodium 
and aluminum and contains a variable proportion of replac- 
ing elements, mainly calcium, magnesium, and iron. It 
crystallizes in the monoclinic system, but almost always 
in irregular masses; individual crystals are rarely seen. 

The crystalline aggregate that gives jadeite its toughness 
possesses a granular texture, which in turn gives the sur- 
face a somewhat dimpled appearance. Though the rough 
surfaces are dull or waxy, the luster of cut and polished 
jadeite is vitreous. Jadeite is the harder and heavier of 
the two jade minerals; a test for specific gravity is often 
used to distinguish between them. 

One of the characteristic gems of mctamorphic origin, 
jadeite is found in dikes in a green serpentine rock. If it 
has been eroded out of place by streams or glaciers, it is 
found as scattered boulders. 

It seems almost contradictory that little jadeite has ever 
been found in China. The material must have been im- 
ported from near-by countries long after nephrite was 
used. Most of the world's jadeite still comes from quar- 
ries discovered in the 1 3th century in the Myitkyina district 
in Upper Burma and is shipped to China by way of Ran- 
goon. The rest of Chinese jadeite came from the moun- 
tains of Turkestan. Most other reported finds may be 
viewed suspiciously, for the whole matter of the identity 
and the sources of both kinds of jade needs restudy. 

Nephrite. The more common of the two jades is neph- 
rite, a member of the awphlbole group of minerals. This 
group closely parallels the pyroxenes, to which jadeite 
belongs, and includes a similar range of elements but only 
one gem material instead of three as in the pyroxene group. 


More specifically, nephrite fits into that part of the amphi- 
boles which is represented by the tremolite-actinolite series, 
the members of which grade into each other according to 
the amount of iron present; when there is enough iron 
to color a specimen green, it is called actinolite. Both of 
them are better known in the form of asbestos, but when 
they are tough and compact they become nephrite. Chem- 
ically, nephrite is a silicate of calcium and magnesium, 
with some iron and water. 

The name comes from the Greek word for "kidney," 
which implies the same curative power as the Spanish 
word for jadeite. New Zealand material is often called 
greenstone, but this is confusing because the same word 
has a different meaning to geologists. 

Nephrite has a smaller range of color than jadeite but 
sufficient to satisfy most preferences. The green color is 
due to ferrous iron. Nephrite is usually more opaque than 
jadeite and hence is less highly valued. Whereas a rough 
piece of nephrite is as dull as a rough piece of jadeite, the 
polished surface takes on an oily instead of a vitreous 

Nephrite crystallizes in the monoclinic system. Its 
structure is distinctly fibrous, the individual fibers often 
being entwined in a most confusing way; nephrite is 
even tougher than jadeite. Much nephrite has a hornlike 

Nephrite, like jadeite, is metamorphic in origin and is 
found in the parent rock, as well as in boulders. 

China furnishes its share of nephrite. Although jadeite 
occurs in Turkestan, as mentioned before, nephrite is much 
more important there. It is also found west of Lake 
Baikal in south-central Siberia. The old question of the 


origin of the carved jade used by the Swiss lake dwellers 
and of similar pieces picked up elsewhere in Europe was 
solved by the discovery of nephrite at several places in 
Silesia. The Maoris of New Zealand obtained their 
nephrite mostly from boulders on South Island. Similar 
nephrite comes from Alaska, where tons of rough green 
and brown material are now being mined each summer 
and brought out by dog teams, airplanes, and small boats. 

In 1946 nephrite moved into the leading place among 
American gems in terms of value of production, owing to 
the continued expansion of jade prospcctirfg in Wyoming 
which began about ten years before. There has been a 
steady improvement in the color and translucency of the 
green stones, and the black ones are being found in larger 
sizes. Both kinds are being shipped to China for carving, 
though most of them are still cut in the United States. 
All the specimens are found as loose boulders on the sur- 
face of the ground. The chief locality is around Lander; 
some nephrite also comes from the Red Desert and the 
Laramie Range. 

Mention should be made of the nephrite deposit in 
Monterey County, California, described in 1940 by Austin 
F. Rogers. 


Russian lapidary art boasts among its achievements the 
creation of lavish carvings in rhodonite. As large an object 
as a royal sarcophagus has been made from it, and a favorite 
gift at court was a rhodonite Easter egg. This opaque 
pink mineral, appropriately named from the Greek word 


for "rose," is moderately hard, and when compact it takes 
a satisfying polish, suitable for beads or cabochons. 

As a manganese silicate, rhodonite is a primary mineral 
which readily alters to black oxides that by the geologic 
processes of concentration often become important ores 
of manganese. The black veins so common in rhodonite 
are evidence that alteration has already begun. 

Although it is often referred to as a member of the 
pyroxene group of minerals, rhodonite can claim only a 
first-cousinly relationship to them. It crystallizes in the 
triclinic system, and occurs both massive and in crystals 
(Fig. 28) having two distinct cleavages. 

Translucent crystals of rhodonite are found in Sweden. 
Most of the material used in Russia was quarried in the 
Ural Mountains. Other massive rhodonite comes from 
New South Wales, and some gems have been cut from the 
unusual zinc-bearing rhodonite at Franklin, New Jersey. 


Pretty gems for pendants and bracelets are cut from 
translucent chrysocolla, which is found in delicate hues of 
green and blue. The luster is either vitreous or enamel- 
like. Chrysocolla is a hydrous copper silicate with a 
variable composition, so that the chemist has difficulty in 
assigning an exact formula to it. Chrysocolla is very finely 
crystalline, like chalcedony quartz, and has not yet been 
assigned to any particular crystal system. 

In the upper zone of copper deposits where it has been 
formed by the alteration of primary minerals, chrysocolla 
is associated with two* other gems, azurite and malachite, 
and serves as a minor ore of copper. It has a world-wide 


distribution; American gems come especially from Arizona 
and New Mexico. 

The name has an interesting origin. It comes from 
two Greek words meaning "gold glue," because chryso- 
colla, or much more probably a mineral resembling it, was 
believed used by ancient jewelers to solder gold. 


Until its present name was internationally agreed upon 
about a decade ago, this mineral was better known as 
"vesuvianite," from its earliest recognized occurrence on 
Mount Vesuvius. Of all the gems it is perhaps the most 
difficult to classify according to the predominant mode of 
cutting. The transparent crystals of prevailingly green, 
yellow, and brown tones, are eminently desirable for 
faceting. The variety calif ornite, however, occurs in com- 
pact green masses like jade. The large amount of this 
latter material that has been cut and polished in the United 
States during recent years has been the deciding factor in 
placing idocrase among the cabochon gems. 

Chemically, idocrase is a hydrous silicate of calcium 
and aluminum with a complex formula that allows for the 
presence of magnesium and iron; other, rarer, elements 
include fluorine, boron, and beryllium. Crystals of ido- 
crase belong to the tetragonal system and often show well- 
developed square prisms (Fig. 16) with striated faces. The 
name of the mineral comes from two Greek words mean- 
ing "form-mixing" because the crystals were mistaken for 
those of other minerals. 

During the metamorphism of limestone to marble, a 
number of new minerals, including idocrase, crystallize. 


The gem associates of idocrase include diopside, garnet, 
and tourmaline. 

Californite is found in Siskiyou, Tulare, and Fresno 
counties in California. When discovered earlier in the 
Swiss Alps it was believed to be jade. Transparent gem 
idocrase comes from Mount Vesuvius and Piedmont Prov- 
ince in Italy, the Tirol, Switzerland, and Siberia. Superior- 
quality gem crystals were found in 1946 in an asbestos 
quarry in northern Vermont. 


Two types of zoisite have been cut and polished for 
their attractive appearance. One is a rose-colored variety, 
called tbulite from the old name for Norway, where it is 
chiefly found; it also occurs in the Italian province of 
Piedmont. Thulite owes its pleasing color to magnanese 
and is cut into cabochons, slabs, and small ornaments. 

The other material is really a mixture of several min- 
erals, of which zoisite is the chief. Known as saussurite and 
named after the Swiss geologist Horace B. deSaussure, 
it is the product of the decomposition of feldspar. Be- 
cause of its resemblance to jade it is substituted on occasion 
for that more valuable gem. 

Zoisite itself is a hydrous silicate of calcium and alumi- 
num; it belongs to the epidote group of minerals but is the 
only one that crystallizes in the orthorhombic system. 


Although an occasional transparent brown pebble of 
Staurolite is taken from the diamond-bearing sands of 


Brazil and faceted into a stone for jewelry, the mineral is 
in gemology more a charm than a gem. Known as "cross 
stone" and "fairy stone/' it has been associated with the 
activities of legendary beings and is widely used as an 
amulet. It seems to be the only gem besides pearl that 
is worn in its original state, with no treatment necessary 
except drilling so that it may be hung on a chain or sus- 


Fig. 91 Twin 

Fig. 92 Twin 

Fig. 90 

Crystals of Staurolite 
[From Hurlbut Dana's Manual of Mineralogy, copyright 1941.] 

pended from a swivel. Some specimens, of course, are 
polished to remove foreign particles adhering to them. 

The crosslike twin crystals of staurolite are unique and 
unmistakable. They consist of two orthorhombic crystals 
(Fig. 90) which penetrate each other; some pairs cross 
nearly at right angles (Fig. 91) and others cross at about 
60 degrees (Fig. 92). In color they are reddish brown or 
brownish black; the choicest specimens are rather red, 
translucent, and symmetrically formed. These crossed 
crystals should not be confused with the chiastolite va- 
riety of andalusite, which owes its cross to inclusions of 


Staurolite is at least as hard as quartz, but this hardness 
has little practical value inasmuch as the stone is so seldom 
cut. Chemically, staurolite is a hydrous silicate of alumi- 
num and ferrous iron, but even reasonably pure specimens 
are rare. 

Staurolite is a characteristically metamorphic mineral, 
associated with other gems, including garnet, tourmaline, 
kyanite, and sillimanite. Excellent crystals are found in 
Switzerland; others come from Germany, Czechoslovakia, 
France, Scotland, and Brazil. In several places in the 
United States, especially along the South Atlantic Coast 
in Georgia, North Carolina, and Virginia, they are picked 
up in abundance. 


Massive, opaque, blue or violet dumortierite takes a fine 
polish and has been cut into flat stones and cabochons. 
The mineral is found also in an attractive pink color 
with strong dichroism, resembling tourmaline. It is most 
valuable, however, as a raw material for the best refrac- 
tory porcelain, and as such it is extensively mined in 
Nevada and California. Gemmy stones are found in 
these and a number of other localities throughout the 

Dumortierite was named for a French paleontologist, 
Eugene Dumortier. It is a silicate of aluminum and boron 
and forms in pegmatite dikes and metamorphic rocks. 
Although it belongs to the orthorhombic system it seldom 
shows distinct crystals; frequently it is found in fibrous 
crystalline aggregates radiating from a center. 



Practically all the gems thus far discussed have been 
carved, more or less frequently, into ornamental objects, 
some of which have utilitarian value also. There is, how- 
ever, a small group of minerals, often mentioned in books 
on gemology, that are almost never suitable for personal 
adornment but serve a wider ornamental and decorative 
purpose. Not to overlook them, a single paragraph is 
devoted to each, but the reader is referred to books on 
economic mineralogy for more adequate descriptions of 


The charm of marble lies in its infinite variety. So 
diverse is this substance that almost any random word- 
picture fits marble from some locality. Figure 29 shows 
dendritic marble. Chemically, marble is calcium carbonate 
(though seldom pure), and geologically, it is metamor- 
phosed limestone. A large part of the marble used for 
such objects as pen stands is sold under the name "onyx," 
which properly applies only to the chalcedony variety of 
quartz, a very much harder and more durable mineral. 
Besides relative softness, marble is characterized by its 
effervescence in acid. 


The massive variety of gypsum, which is calcium sul- 
fate, is called alabaster, though in ancient times alabaster, 
as used in the Bible, meant the material that we now call 


marble. Owing to its softness the mineral is easily carved. 
Vases and boxes of white Italian alabaster are well known. 
In the United States, especially in Colorado, alabaster is 
worked into lamps and other articles that adapt themselves 
nicely to its white color and brown or gray veining. Satin 
spar, which occurs in monoclinic crystals like that in Fig. 
25, has a fibrous structure; many necklaces fashioned from 
this variety of gypsum have been sold at tourist resorts, 
notably Niagara Falls. 

Sepiolite (Meerschaum) 

The German word meerschaum means "sea foam" and 
is properly descriptive of this porous, whitish mineral 
found floating in the sea. The material to which this 
name is applied seems to be a mixture of some amorphous 
substance and a fibrous mineral known as sepiolite, which 
is a hydrous silicate of magnesium. It is derived from the 
alteration of serpentine; by far the most important source 
is Asia Minor. Meerschaum, because it is easily carved 
and capable of taking a pleasing polish, has been used 
considerably for pipe bowls. 


When mottled in dark and light green, corresponding 
in appearance to a serpent's skin, from which it gets its 
name, serpentine makes an attractive decorative stone be- 
cause of its lively patterns and its oily or waxy luster. It 
is a hydrous silicate of magnesium and is found abundantly 
throughout the world as an alteration product of olivine 
and other magnesium silicates. It crystallizes in the mono- 


clinic system, but no original crystals have ever been seen. 
Serpentine is usually found in masses consisting of a platy 
mineral known as antigorite. Boivenite is a compact va- 
riety of this same substance and resembles jade; material 
from China and New Zealand is carved and sold as jade. 
When serpentine is fibrous it is called chrysotile, which is 
the chief kind of commercial asbestos. 

Miscellaneous Jadelikc Minerals 

Several minerals that resemble jade have already been 
discussed. Most of them are gemstoncs in their own 
right, a jadelike variety being an "added attraction." 
These minerals include quartz, feldspar, serpentine, preh- 
nite, garnet, idocrase, zoisite, and sillimanite. 

A few materials not otherwise mentioned in gemology 
have more or less frequently been carved and sold as jade. 
They may be appropriately described here under "Orna- 
mental Stones." 

Compact pieces of the mineral pectolite, a fusible hy- 
drous silicate of calcium and sodium, are carved into orna- 
ments and implements by the Eskimos of Alaska. 

In a rather different category from pcctolite belong 
some materials which are soft enough to be worked with 
a knife. They are familiar in cheap Oriental objects, 
but the names given to them are not standardized and 
are often confusing. Some of the materials themselves, 
moreover, are not homogeneous, and hence the same 
name may apply to several different natural mixtures of 

Soapstone carvings, such as vases, ash trays, and animal 
figures, make up a large part of every stock of Chinese 


articles. Soapstone is the popular name for steatite, a 
soapy-feeling compact variety of talc, which is a mono- 
clinic hydrous silicate of magnesium at the very bottom 
of the hardness scale. The mineral saponite, which is a 
hydrous silicate of aluminum and magnesium, also is called 

Similar to these (and including some steatite) is a ma- 
terial known as agalwatolite, though the name is seldom 
used; most of the objects made from it are called soap- 
stone, "figure stone/' or "pagoda stone." The last two 
names are appropriate because the Chinese use it so pro- 
fusely for images and replicas of pagodas. Agalmatolite 
is actually steatite, pinite, pyropbyllite, or indefinite mix- 
tures produced by the alteration or decomposition of vari- 
ous silicate minerals. 


Chapter 5 

Gems of the Silica Group 

Silica is the chemical term for a stable compound of 
silicon and oxygen that occurs everywhere in both the 
organic and the inorganic world. Three minerals quartz, 
tridymite, and cristobalite each existing in several modi- 
fications, are composed of silica. A fourth mineral, opal, 
consists of silica and a varying amount of water. Of these, 
quartz and opal are among the most important of all gems. 
In addition, though not true minerals and hence not part 
of the silica group, there may properly be included in this 
chapter three kinds of natural glass containing high 
amounts of silica and having some use in gemology. 

The quartz gems lose none of their beauty because they 
happen to belong to the most abundant of the mineral 
species. Besides many common and industrially useful 
varieties, quartz boasts a number of splendid gems, without 
which the jeweler's window as well as the mineral king- 
dom would be immeasurably poorer. A large part of the 
mineral specimens collected yearly in the United States by 
enthusiastic hobbyists, and most of those cut into gems 
by amateur and professional lapidaries, are quartz. In 
hardness quartz ranks number 7 in the standard scale 


and serves to demarcate the hard gemstones from the 
soft ones. 

Gems are furnished by two main types of quartz, which 
differ mainly in the degree of fineness which their struc- 
ture has assumed. The crystalline varieties quartz proper 
are rather glassy in appearance, are more or less trans- 
parent, and frequently occur in good crystals. The cryp- 
tocrystallme (crypto means "hidden") or chalcedony va- 
rieties do not show external faces but are nevertheless com- 
posed of exceedingly small crystals in a microscopically 
intimate aggregate which gives them a compact, flinty 
look. Much controversy has arisen about whether chal- 
cedony should be regarded as a distinct mineral or as a 
mixture of quartz and opal (hydrous silica gel). Its 
hardness, specific gravity, and other properties are slightly 
lower than those of crystalline quartz. Inasmuch as the 
general differences between the two are such as to make 
one (quartz) suitable for faceting and the other (chal- 
cedony) for cutting into cabochons, in accordance with 
the major divisions of this book, it is becoming customary 
to refer to them as separate gem minerals. 


The typical crystal of quartz (Fig. 93) is easily recog- 
nized by its six sides which, when they are complete, come 
to a point at one or both ends. A frequent aid to identifi- 
cation is the presence of horizontal lines or striations on 
the prism faces. Quartz crystals range in size from tiny 
ones in groups to single crystals weighing a ton. Much 
quartz of the crystalline type is found in irregular masses 


that fail to show crystal faces; but the precise regularity 
prevails internally. 

Fig. 93 Group of Quartz Crystals 

[Ward's Natural Science Establishment.] 


The most valuable quartz gem is amethyst. Its in- 
comparable color varies from a delicate orchid to a glori- 
ous purple unsurpassed in the realm of nature. The name 
comes from the Greek word meaning "not drunken," sup- 
posedly because the stone was believed to prevent or cure 
intoxication; Pliny wrote that the name was given because 
the color approached but did not equal the hue of wine. 


Until the discovery of large deposits of amethyst in 
South America, the stone was considerably more expensive. 
Only its relative abundance can account for the present 
reasonable cost of so lovely a gem. For amethyst has been 
highly praised for thousands of years, and from it have 
been carved works of art of the highest excellence. Those 
from Egypt include charms, vases, and shells; Etruscan 
and Roman specimens are principally intaglios of pale 
tint. Splendid examples of amethyst sculpture include a 
bust of Trojan which was taken from Berlin to Paris by 
Napoleon, the Blacas Medusa head, and miniature repro- 
ductions of the Apollo Belvedere, the Farnese Hercules, 
and the Laocoon groups. 

One of the most famous pieces of historical jewelry is 
the necklace of fine amethyst beads worn by Queen Char- 
lotte of England in the days before the gem began to lose 
its rarity. Catherine the Great was an ardent collector 
of amethysts. Her unrivaled collection of them was se- 
cured from mines in the Ural Mountains by thousands 
of slaves and laborers. The most beautiful amethysts were 
placed among the crown jewels, settings for which were 
designed by French jewelers, and they were the boast of 
Catherine's successors until many of the finest were sold 
in 1906. The rest are in the possession of the Soviet gov- 
ernment, according to an inventory made in 1925 by a 
German mineralogist, who described them as "glowing 

The structure of amethyst represents an intricate ar- 
rangement of twinned particles. The color is usually in 
layers and patches, and seems to be due to iron present 
as an impurity. 


Amethyst is the national gem of Uruguay. The de- 
posits extend into neighboring Brazil and constitute the 
most notable source of amethyst in the world. Gems of 
the richest hue have come from Siberia. Ceylon and 
Japan have provided good crystals. In the United States 
fine specimens of amethyst have been found in half a 
dozen states; major places include Amherst County, Vir- 
ginia, Alexander and Lincoln Counties, North Carolina, 
Keweenaw Peninsula, Michigan, and Jefferson County, 


This is perhaps the only gem named for its imitation. 
Several centuries ago a bowl of copper filings fell by acci- 
dent into a pot of molten glass in a factory near Venice. 
The brightly colored glass was so attractive that it was 
made into ornaments and called aventurine, from the 
Italian word for "chance." Many years later a natural 
substance of similar appearance was discovered and was 
also named aventurine; it proved to be a variety of quartz. 
The imitation material is widely sold in novelty jewelry 
as "goldstone." Aventurine is usually green, brown, or 
red quartz, spangled with flakes of mica or hematite. The 
Soviet Union and India are the most noted sources. 


Yellow quartz is named citrine from the Latin word for 
"lemon," but its color is usually somewhat more brown- 
ish than that of the fruit. It looks so much like topaz 
that these two entirely distinct minerals have long been 


confused. The difference between them is still not 
thoroughly realized, even by many jewelers. The sig- 
nificant contrast between the two is really their cost; a 
purchaser cannot expect to find the much rarer true topaz 
in moderately priced jewelry, and therefore should assume 
that the word topaz when unqualified is usually being 
used incorrectly to mean citrine. 

Ferric iron oxide is the cause of the color, which ranges 
from yellowish green to yellow and reddish orange. These 
hues are sometimes obtained by heating darker, inferior 
varieties of quartz. Brazil produces most of the world's 
supply of citrine, though some comes from Madagascar. 

Rock Crystal 

Clear lustrous quartz, without any color, is known as 
rock crystal. When first discovered high in the Alps it 
was believed to be a "kind of ice" (krystallos), that is, 
water permanently frozen into a definite form by the ex- 
cessive cold. The word crystal, now applied to any regu- 
larly shaped mineral, came from this erroneous idea. So, 
in a sense, this variety of quartz was the original "crystal." 

Under that name it appears as spheres (Fig. 94) for the 
hypnotic art of crystal gazing. Displayed in the United 
States National Museum is the largest crystal ball in the 
world, a perfect globe weighing 107 pounds. The ex- 
tensive use of rock crystal in optical, radio, and radar loca- 
tion instruments is a phenomenon of World War II. Cut 
into thin plates it controls frequencies by means of its 
very rapid and very regular vibration. As crystals must 
be free from internal twinning, the supply is limited almost 
entirely to Brazil. Rock crystal is also used for eye-glasses 


on account of its hardness and for camera lenses because 
of its transparency to ultraviolet rays. 

Its popularity as a gem is especially evident in the 
many bead necklaces that have been made from it. Rock 

Fig. 94. Rock Crystal Sphere 

The boulder from which it was cut was found in the soil at Phila- 
delphia. [From Hawkins The Book of Minerals, copyright 1935.] 

crystal seals and ornamental carvings are prized in leading 

Its abundance makes rock crystal the most common 
transparent gem. Great quantities of large crystals come 
from Brazil. Madagascar and Japan, as well as the Alpine 
countries of Europe, have furnished much high-quality 
material. The Arkansas deposits near Hot Springs are 
the most prolific in North America, and the exquisite little 


crystals called "Herkimer diamonds" that used to come in 
large numbers from Herkimer County, New York, are 
surely the choicest. 

Rainbow Quartz 

Rock crystal made iridescent by cracks which separate 
the light into its spectrum colors is known as iris or ram- 
bo<w quartz. This minor variety can be imitated by the 
sudden cooling of a heated stone. 

Milky Quartz 

The presence of many liquid inclusions reduces the 
transparency of rock crystal and causes a milky appear- 
ance which justifies the name milky quartz. 

Gold Quartz 

During the great gold rushes of the 19th century a large 
quantity of milky quartz containing particles of gold and 
hence called gold quartz was cut for jewelry as souvenirs 
of the mining camps. 


Rock crystal that encloses needlelike crystals of other 
minerals, such as tourmaline, rutile, actinolite, or goethite, 
constitutes the variety known as sagenite. Several names 
that are more romantic are also used Venus Vhairstone, 
arrows of love, and Cupid's darts. 



When the inclusions of other minerals in quartz be- 
come so closely packed that they seem to predominate 
over the quartz itself, and especially when they are pres- 
ent in thin parallel fibers like asbestos, the chatoyant va- 
riety known as cat's-eye is formed. A band of light at 
right angles to the fibers follows the gem as it is turned. 
This stone should really be called quartz cafs-eye to 
distinguish it from cat's-eye of the chrysoberyl kind 
(already described under that species). The two gems 
resemble each other somewhat, but the chrysoberyl is 
superior in value because of its more lustrous beauty. 
Green, brown, and yellow quartz cat's-eye, mostly with a 
grayish cast, comes from Ceylon, India, and Germany. 


When the quartz itself, rather than its inclusions, is 
fibrous, two other varieties of "eye stones" tiger's-eye 
and hawk's-eye are produced. 

Tiger's-eye is unique among gems, a golden brown stone 
with wavy bands of light which move glowingly across 
the surface when it is rotated. Originally it was a blue 
kind of asbestos called crocidolite, but the coloring matter 
has been oxidized and the mineral completely replaced 
by quartz. Preservation of the earlier fibrous structure 
causes the handsome rippling effect known as chatoyancy. 
When first found, tiger's-eye (or tiger eye} brought a high 
price, which declined drastically upon the discovery of 
large deposits of the material. However, it still comes 
from only one place in the world, Griqualand West in 


South Africa. Cut into cameos for men's rings, it has been 
one of the most popular stones of recent years. 


Crocidolite similarly turned into quartz but without 
changing its blue color in the process is called hawk's-eye. 

Rose Quartz 

Its lovely hues of pink and rose red, caused by the pres- 
ence of manganese, make rose quartz one of the prettiest 
of the translucent gcmstones. It occurs in irregular masses 
without crystal faces. In spite of being very difficult to 
handle because it breaks into angular pieces with jagged 
edges, it is often worked into beads, small ornaments, and 
cabochons. The Scott mine near Custer, South Dakota, 
is a huge quarry of rose quartz, but material of ornamental 
quality is scarce even there. Other sources include South- 
West Africa and a few of the many deposits elsewhere 
that yield the more common quartz gems. 

Smoky Quartz 

A pleasant surprise is in store for everyone who looks 
for the first time through a crystal of smoky quartz and 
sees an apparently opaque black stone become a mys- 
teriously hazy but rich shade of brown as the light comes 
through. The cause of this color is ascribed to radioactive 
emanations within the rocks. Smoky quartz has been 
found so frequently in association with uranium and other 


radium-containing minerals that this relationship seems 
most plausible. Furthermore, clear rock crystal takes on 
a smoky hue when it is bombarded experimentally by 
X-rays and other powerful short-wave rays. 

Lighter hues of smoky yellow, grading into citrine, are 
known as cairngorm, a Scottish name for a gem so popu- 
lar in that country that it is regarded as a national stone. 
Smoky quartz grades in the other direction to a black stone 
known as morion, used occasionally in mourning jewelry. 

These varieties of quartz are not widespread. The Scot- 
land cairngorm deposits of the Highlands are virtually de- 
pleted. Excellent smoky quartz comes from the Swiss 
Alps, Spain, and the Pikes Peak region of central Colorado. 


The term chalcedony embraces an extensive group of 
gems in a wide range of colors and with a bewildering 
array of names. All these stones have a crypto crystalline 
structure, but some are fibrous and some are granular, 
although it is usually impossible to distinguish between 
them without a microscope. 

Unlike many of the varieties of crystalline quartz, the 
chalcedony gems are characteristically translucent or 
opaque rather than transparent. They have a compact 
appearance and a waxy luster, and occur most frequently 
in rounded and imitative forms or as cavity linings. 

No single classification of the cryptocrystalline quartz 
gems has ever satisfied all mineralogists or jewelers. Sev- 
eral of the major varieties are much better known than 
the general name chalcedony, which is little used for any 


particular stone. A convenient system of nomenclature 
that is gaining in favor puts only light-colored gray, blue, 
milky-white, and yellowish-brown stones that have no 
other special names under chalcedony proper and applies 
other names, such as agate and jasper, to the more signifi- 
cant colors and patterns. The distinction between the 
varieties of chalcedony is, in fact, based almost exclusively 
upon color and pattern, a reminder of the days when they 
were all regarded as quite different substances because they 
look dissimilar. 

The chalcedony gems have been the chief medium for 
engraving since the beginning of that art. The current 
popularity of amateur gem cutting in America affects this 
group of stones far more than any other, because they are 
so abundant, inexpensive, and varied, and can be worked 
without too much difficulty, yet offer the lapidary a 
reasonable degree of hardness. The prevailing mode of 
cutting is cabochon, but carved objects of all sorts, from 
spheres and transparencies to simple ornaments and intri- 
cate novelties, are made from chalcedony. 


Red chalcedony, varying in hue from pink to blood red 
and from honey yellow to orange, and colored by ferric 
iron oxide, is called carnelian or cornelian. No other gem 
has been carved into so many seals and signet stones, and 
carnelian beads have been popular for centuries. The 
smooth, lustrous polish that carnelian takes is one of its 
chief delights. Noted sources are India and Brazil, and 
good stones have come from Tampa Bay in Florida. 



When the color of chalcedony approaches brown, 
carnelian grades into sard, which is just as well known 
by name, although the Biblical references to this gem 
probably referred to the true red carnelian. Sard was 
worked also by ancient and Renaissance craftsmen. 


Apple-green chalcedony, nicely colored by nickel oxide, 
was once considered the most beautiful variety. The name 
for it, chrysoprase, is derived from the Greek words 
meaning u golden green." After the exhaustion of the 
deposits in Silesia, over a hundred years ago, this gem 
became rare and consequently was extensively imitated. 
Rather recent discoveries of chrysoprase in California and 
Oregon have helped to restore the genuine material to 
public attention. 


Although some prase is clear crystalline quartz contain- 
ing many green fibers of the mineral called actinolite, the 
name prase is also applied to chalcedony the color of which, 
like that of chrysoprase. is green. Prase, however, is more 
like sage green and is duller in tone. The best stones 
have come from Saxony, Germany. 



A gem similar to prase, but often bright grass green in 
color, is called plasma. A frequent characteristic of this 
stone is the presence of white or yellow spots on the 
green background. 


The combination of red and green in one gem gives us 
bloodstone. Irregular spots of red, resembling drops of 
blood, against an otherwise solid body of dark green, make 
this one of the really unusual stones. Remarkable portray- 
als of the Crucifixion have been carved in bloodstone, and 
it serves well in men's signet rings. Another name for 
the gem, common in Britain but not in America, is helio- 
trope. India furnishes the best bloodstone, and other fine 
specimens come from the Ural Mountains. 


Almost any color may mark the presence of jasper, for 
this general name is applied to the deeply colored varieties 
of chalcedony which are virtually opaque because of an 
excess of coloring matter. Such impurities are usually red, 
brown, yellow, or green and are due mostly to iron oxides 
which appear in patches or bands. The name ribbon 
jasper identifies a stone with broad varicolored stripes. 
Egyptian jasper has yellow or brown zones. Some inter- 
esting rocks known as conglomerates contain rounded or 
angular boulders of jasper. In spite of its commonness, 
jasper has been carved into a number of rather valuable 


art objects, particularly in Russia, where Siberian mate- 
rial with alternating red and green stripes has been much 

Moss Agate 

Although moss agate does not contain any moss, either 
plant or fossil, it preserves an eternal landscape in stone. 

Fig. 95 Typical A loss Agate from Yellowstone River, 


(See Fig. 95.) The fascination found in these intricately 
branching designs is hard to surpass in the whole realm of 
gemology. Realistic scenes of mountain and lake, coast 
and forest, park and stream suddenly spring into view as 
the lapidary removes the outer layer or "skin" and moistens 
the stone. Mineral matter, usually manganese oxide or 
sometimes iron oxide, spreads out to form dendritic or tree- 
like patterns in this variety of chalcedony. The prevailing 
color is black or brown, but sometimes the impurity con- 
sists of fibers of chlorite which present a tangle of green 


resembling seaweed; sometimes moss agate shows a splurge 
of spectacular colors. 

The great variety of designs to be found in agates of this 
sort has given rise to an equal variety of names. Gems 
from India are called Mocha stone. Terms such as flower 
agate, plume agate, scenic agate, landscape agate, seaweed 
agate, and tree agate are representative of the almost count- 
less descriptive and local names that are current in one 
place or another. As is true of most of the varieties of 
chalcedony, American moss agate is found in its greatest 
profusion in the western states; Montana, along the Yellow- 
stone River (Fig. 95), and Wyoming, along the Sweet- 
water River, arc the most noted. Miniatures carved from 
American moss agate are shown in Fig. 53. 


The term agate may include the moss agates just de- 
scribed as well as chalcedony in which the color is dis- 
tributed in irregular patches, as in many of the well-known 
thunder egg nodules (Fig. 96) of Oregon and California. 
But the proper use of the word agate is restricted to chal- 
cedony in which the colors are laid out in wavy concen- 
tric bands which conform to the cavity of the volcanic 
rock in which the silica was originally deposited. Constant 
or recurrent changes in the nature or degree of the im- 
purities that produce the coloring matter are reflected in 
the successive layers as they build up the stone. The bands 
may differ in thickness or they may be fairly uniform for 
a considerable distance. An infinite variety of patterns 
and colors is the result; see Fig. 97. 


Interesting names are given to these variants according 
to the design, which often depends solely upon the direc- 
tion in which the stone is cut. If, for example, a rounded 
specimen is sectioned across the layers, a face of the stone 

Fig. 96 Oregon Thunder Egg 
Sawed and polished specimen partly filled with agate. 

may show complete rings surrounding a solid center, like 
a target; such a piece is called an eye agate. Fortification 
agate (Fig. 98) has angular bands whose outline imitates 
the ground plan of a fort. Iris agate appears colorless until 
held in the proper direction toward the light, when sud- 
denly a swirl of rainbow colors comes into view, owing to 
the diffraction of light from extremely closely spaced 


parallel layers. The term banded agate is more or less 
redundant, if the limited definition of agate is accepted. 
The word agate itself came from the river Achates (now 
the Drillo) in Sicily, along the banks of which the earliest 
stones were found. 

The town of Idar-Oberstein in Germany was once noted 

Fig. 97 Polished Agates Showing Growth Structures 

Top specimen, Brazil; lower specimens, Wyoming and South Dakota. 
[Rushmore Afuseum.l 

for the finely colored agates found in the vicinity. The 
skill that the inhabitants acquired in cutting them for the 
trade was soon applied to other kinds of stones and they 
developed the world's largest gem-cutting industry. As 
the local deposits of agate diminished, some of the lapidaries 
moved elsewhere. A few of the emigrants went to South 
America, where they became acquainted with the vast 
quantity of pale agates in Uruguay and southern Brazil. 
These were sent back to Germany for cutting, and from 
the newly discovered and apparently limitless source of 


supply came the impetus to experiment with artificial meth- 
ods of enriching the color on a commercial scale. 

The natural colors of few agates compare in vividness 
with those obtained by soaking the stones in certain chemi- 

Fig. 98 Superb Fortification Agate 

cals, and one may safely assume that any brightly colored 
agate has been thus treated. The principle underlying this 
process is that the layers of silica that constitute agate are 
porous in varying degrees, so that some layers take up 
certain coloring matter while other layers remain un- 
affected by the same chemical. After years of experimen- 
tation a fairly standard sequence of treatment has evolved, 


although each sample has to be tested to determine its 
possibilities. During World War II, when German prod- 
ucts were unavailable, agates from hundreds of domestic 
localities were examined by American dealers with the dis- 
covery of only a few stones that proved to be susceptible 
to systematic improvement in color. 

Besides agate, other varieties of porous chalcedony may 
be stained attractive colors, but the chief result has been 
to simulate some more popular gem. Perhaps the most 
important examples of such artifice are the production of 
green "chrysoprase" from agate or ordinary chalcedony 
and of blue "lapis lazuli" from jasper. 


When the layers of agate are straight, parallel, reasonably 
wide, and of conspicuously contrasting colors, the term 
onyx is properly used. The sharply defined colors provide 
the gem engraver with a most suitable medium for cameos 
with a head of one color on a background of another. 
Modern cameos are carved largely in stained chalcedony, 
but the natural colors of many ancient gems are satisfy- 
ingly rich. The most typical arrangement consists of a 
white head against a black field. The word onyx is often 
used to refer merely to black chalcedony, which has for 
centuries been produced by soaking the stone in honey 
or in a sugar solution and then charring the sugar with 
sulfuric acid; a superior new process, employing cobalt 
nitrate and ammonium sulfocyanide, was described by 
George O. Wild in 1947. True onyx, however, is chal- 
cedony of more than one color. 



Sardonyx is therefore onyx having a combination of 
sard (or its more reddish cousin, carnelian) and chalced- 
ony of another color, usually white or black. It too is a 
popular stone for cameos. 

Petrified Wood 

Wood turns to stone even to gemstone when silica- 
bearing waters, percolating through the ground or rising 
from cooling bodies of rock below, reach a place where 
trees have been submerged and preserved from decay and 
deposit their mineral matter in the cells of the trunks, 
branches, and twigs. In the process they usually replace 
the woody substance and carry it away but preserve the 
plant structure, often with such remarkable fidelity that 
the species of tree can be identified. 

Although many minerals replace wood, by far the most 
abundant replacement is chalcedony. Hence the term 
petrified wood is virtually synonymous with silicified 
'wood. Opalized wood is the same product if the silica is 
present in the hydrous noncrystalline state called opal. 
Petrified wood so frequently exhibits regular banding or 
the swirling patterns of cloudy agate that the name aga- 
tized wood is very appropriate. Large patches of bright 
colors give the name jasperized wood. 

Petrified forests and smaller areas of petrified wood are 
rather widely distributed, though much less so than the 
profusion of original timber suggests. Each deposit has 
its own characteristic features such as the kind of tree, the 


range of size of the logs and limbs, the state of preserva- 
tion, the presence or absence of bark, and the colors. 

Petrified Forest National Monument and adjacent areas 
in Arizona have furnished the major part of the world's 
silicified wood for gem purposes. Reddish-brown, cherry- 
red, and black colors are the most distinctive. The stone 
trees lie at random over a large region, as if they had once 
been driftwood. 

Petrified wood is found to some extent throughout the 
American West. The small black and white limbs and 
twigs from Eden Valley, Wyoming, and the handsome 
specimens from the Cycad Forest National Monument in 
the Black Hills of South Dakota are surely outstanding. 
The central and the eastern states yield petrified wood 
from a number of localities, the oldest in geologic time 
being in the Catskills of New York. Excellent petrified 
wood is found also in Canada, in Patagonia, and elsewhere. 

Besides these gems and ornamental stones, some of which 
also have their everyday industrial uses, quartz and chal- 
cedony include other materials deserving mention for their 
extensive commercial applications. 

Sand, which is usually composed almost entirely of 
quartz grains, is used in the manufacture of glass and 
cement and as an abrasive and flux. Gravel, consisting of 
coarser fragments of quartz, is used in road construction. 
Natural aggregates of quartz in the form of sandstone (a 
sedimentary rock) and qtiartzite (a metamorphic rock) 
constitute important building and paving stones. Itacolu- 
n?ite is a curiously flexible sandstone "the rock that bends' 1 
found in India and North Carolina and associated with 
diamond in Brazil. Flint, a form of chalcedony quartz 


having a conchoidal fracture, was vital to primitive man 
for his weapons and implements and later as a means of 
striking fire. 


Opal is unique in the gem kingdom. It has little color 
of its own, yet shines forth in the radiant splendor of all 
the other gems, combining the reddest red, the bluest blue, 
the greenest green, and every possible hue in its purest 
quality. Because the colors of opal are due to the inter- 
ference of light rays, rather than to the absorption of a part 
of white light, they are of spectral purity and intensity. 
Ruskin wrote that opal "shows the most glorious colors to 
be seen in the world, save only those of clouds." In Roman 
times opal was, next to emerald, the most valuable gem, 
and the naturalist Pliny related that Mark Antony exiled 
a wealthy senator, Nonius, because he refused to sell an 
opal the size of a hazel nut. The name of the gem comes 
from the Sanskrit word meaning "precious stone." 

The enthusiasm which opal arouses in artists and poets 
is not too extravagant. Opal is probably the most difficult 
of all gems to describe adequately to someone who has 
never seen a specimen, especially since there are several 
varieties of precious opal, conspicuously different from 
each other. All of these share an unsurpassed play of 
color as their chief mark of distinction. 

White opal scintillates against a solid background, which 
is always light, either white or tinted some pale color. 
Black opal, on the contrary, has a dark background sel- 
dom really black but usually blue or gray which serves as 
a perfect foil for the colors superimposed on it. Fire opal 


is rather transparent and has a red, orange, or yellow body 
color against which some opalescence is displayed. Coin- 
inon opal includes the many kinds of opal that lack a play 
of color. 

Opal is a mineral, but it is the only one among the gems 
that is virtually amorphous, having only the slightest regu- 
larity in its internal structure. Hence it is not found in 
crystals but prefers to grow in irregular and imitative 
shapes, which often fill cavities in rock, coat surfaces of 
other minerals, or even replace the other minerals. 

In composition opal is hydrous silica; its content of water 
ranges generally from 6 to 10 per cent in precious opal, and 
to 21 per cent in common opal. The opal material is de- 
posited as a jelly from natural hot waters or hot springs. 
As it cools it hardens and loses part of its original water. 
This solidification produces cracks, which may become 
filled with other opal material. When the new opal con- 
tains even a slightly different amount of water it has a 
different refractive index. Within the stone layers are 
built up which reflect the light rays in such a way that they 
interfere. (The same interference causes the colors of 
soap bubbles.) The particular color that is obtained de- 
pends upon the thickness and uniformity of the layers 
and the direction in which they are viewed. The effect 
produced by the interference of light rays is often called 
"fire," but the term should be restricted to dispersion. 

Opal must be handled with care. Besides being rather 
brittle it is not especially hard. Furthermore, it absorbs 
ink and grease; conversely, it may lose water and disinte- 
grate. Heat, even more than dryness, is its dangerous 


White Opal 

The precious opal of the ancients was white opal. It 
is often referred to as Hungarian opal because of the source 
of the Roman gems, as well as of many in our own times. 
The actual locality is at Marmaros in the Nagy Banya dis- 
trict of present Czechoslovakia; the usual reference is to 
Czernowitz, but that town (spelled variously) is about 
200 miles from the mines and is really the marketing and 
cutting center. 

The light background of white opal may actually be 
yellow, pink, or some other light color, according to the 
impurities that were picked up by the silica. Since opal 
may show any hue, special names are given to stones char- 
acterized by certain colors or patterns. Harlequh? opal 
has even patches of color like a mosaic. Lecbosos opal 
has a deep-green play of color. 

In 1889 the rich opal deposits of the continent of Aus- 
tralia were brought to public attention when a hunter 
picked up a fine specimen while he was trailing a wounded 
kangaroo. This place became known as White Cliffs and 
is in New South Wales. In 1915 the Goober Peby or 
Stuarts Range field in South Australia began to supply 
choice white opal. A minor source of white opal is 

Black Opal 

A superior black opal should not be ranked below any 
other gem. The "smothered mass of hidden fire" that 
flashes from it shows more wonderfully because of the 
dark background, as fireworks or meteors appear to best 


advantage at night. Black opal that is actually black is 
exceedingly rare; the typical color is dark blue or gray, 
depending upon the impurities, of which iron is the most 

Black opal was unknown until the discovery in 1905 of 
the fabulous Lightning Ridge field in New South Wales, 

Fig. 99 Rainbow Ridge Opal Mine, Virgin Valley, Nevada 

Australia. Other discoveries near by and in adjacent 
Queensland followed. A find of black opal in Humboldt 
County, Nevada, made the United States an opal producer. 
Among the fine gems taken from that field is the magnifi- 
cent Roebling opal now in the United States National 
Museum in Washington. The mine that furnished it is 
shown in Fig. 99. Unfortunately, Nevada opals often 
develop a multitude of fine cracks upon exposure to the 

The occurrence of the Australian and American black 
opal is very different from that of the Hungarian stones. 
Some of the best material is found in organic remains, 


replacing fossil wood, shells of former sea animals, and 
bones of extinct reptiles that inhabited the land geologic 
ages ago. The tendency of black opal, particularly, to be 
deposited in very thin seams makes it often necessary to 
include a piece of the country rock in the finished gem to 
provide a substantial support; such stones are called opal- 
matrix. Opal doublets, which have a thin slice of opal 
cemented to a backing of plain opal, black chalcedony, or 
glass, are fairly common in good jewelry. 

The current scarcity of black opal marks the end of 
another cycle in the fortunes of this gem. Once highly 
prized, it fell into disfavor after the publication of a novel 
by Sir Walter Scott in which an enchanted opal was the 
cause of tragedy. Queen Victoria revived the popularity 
of opals by bestowing them as wedding gifts and thereby 
aided the development of the newly opened Australian 
mines. Now the deposits "down under" are nearing de- 
pletion; we are left with the discouraging thought that, 
except as family heirlooms and museum pieces, this glori- 
ous gem mav soon become only a memory. 

Fire Opal 

Owing to its transparency, fire opal is the only variety 
of opal that may be appropriately faceted. At its finest it 
is only slightly milky. The play of color is usually hidden 
deep within the stone, disguised by the overall red to 
yellow color. A combination of red opalescence and red 
background is most desired. The mines near Queretaro 
and elsewhere in Mexico are the major source of fire opal, 
though some has been reported from Asia Minor. 


Common Opal 

A transition from precious opal with its play of color to 
common opal without any play of color is exemplified by 
hydrophane, which sometimes shows opalescence only 
after it has been immersed in water. 

Many of the other varieties of common opal resemble 
chalcedony and bear similar names. Thus prase opal is 
green, jasper opal is brownish, agate opal is banded, and 
woss opal has dendritic mosslike inclusions. Other varie- 
ties also have descriptive names, such as resin opal which 
has a resinous luster, and rose opal which is pink. Cacha- 
long is a curious opal considered valuable in the Orient; 
it is so porous that it adheres to the tongue. Hyalite is 
clear and glassy. Better known to geologists are geyserite 
or siliceous sinter, which is common opal deposited by hot 
springs and geysers; and tripolite or diatowaceous earth, a 
chalky material formed in the sea from the shells of 
diatoms, a kind of algae. 


Faceted gems of pleasing color but little value have 
been cut from three types of natural glass found at the 
surface of the earth. 


Obsidian is the chief of these natural glasses. It is the 
result of the very rapid cooling of a volcanic lava, which 
would have formed granite or a related rock if it had 
solidified within the crust instead of flowing out upon 


100 Aztec Obsidian Blades, Mexico 

f Middle American Research Institute.] 


the ground. Obsidian closely resembles artificial glass 
and breaks with a similar conchoidal fracture (Fig. 51) 
and sharp edges; these qualities made it a necessity to an- 
cient peoples, who used it for knives, arrowheads, mirrors, 
and countless other everyday objects. Blades of Aztec 
manufacture are shown in Fig. 100. Obsidian of many 
colors has been found, but most of the faceted gems have 
been cut from green specimens, whereas darker pieces are 
usually cut with rounded surfaces. A glass, obsidian is 
amorphous, of no definite internal structure. Its chemical 
composition is likewise variable but always high in silica. 
Obsidian is common in volcanic regions; such localities 
include Nevada, California, Arizona, Yellowstone National 
Park, several Mediterranean islands, Mexico, Iceland, and 


A kind of natural glass, called silica-glass because it con- 
tains almost 98 per cent of silica, was discovered in the 
Libyan Desert in Africa in 1932. It had evidently been 
worked in sundry ways by the craftsmen of some prehis- 
toric race. Large transparent, light yellowish-green pieces 
have been found. Their origin is a mystery, and only a 
fall from the sky seems an adequate explanation. 


The third type of natural glass is the tektites, which are 
known by several local and regional names according to 
the places in which they are found. Of these, moldavite 
from Bohemia and Moldavia is the best known and has 


long furnished transparent green gems sold as "bottle 
stone." Other sources are Australia, Borneo, and else- 
where within a single narrow zone that crosses the earth. 
Because they do not occur in association with volcanoes, 
like the volcanic glass obsidian, and their peculiar surface 
markings and rounded shapes suggest a prolonged whirling 
motion through the air, an origin outside our own planet 
has been proposed. 


Chapter 6 

Gems with a Genealogy 

The four gemspearl, coral, amber, and jet which trace 
their ancestry to living things are not truly minerals, inas- 
much as they have originated through organic activities of 
nature. Nevertheless, the first two contain mineral mat- 
ter, and the constitution of the other two lies not far out- 
side the scope of mineralogy. Surely all of them must be 
considered gems and deserve our serious attention. Among 
them they divide the earth, for two are gems of the sea 
and have an animal origin, whereas the other two are gems 
of the land and are derived from vegetation. The mys- 
terious processes of life that have given rise to these gems 
make them more remarkable than the gems that have come 
to us from the depths of the earth or the outer vastness 
of cosmic space. 


The Queen of Gems rules supreme amidst the rich 
treasures of Neptune's domain. She has had no rival for 
her throne since the early day when she was first revealed 
to the race of men in her pristine beauty. Adorned only 
with a natural lustrous covering and needing no prepara- 


tion or treatment, except perhaps to be drilled for string- 
ing, pearl has excited the admiration and aroused the 
avarice of men, no less than of women, for millennia. 
Though the pearls of the ancients have not survived, as 
have the more durable mineral gems, their poets and writ- 
ers have recorded in imperishable words their love of this 

Illumined by an iridescent surface, pearl presents a wide 
array of delicate tints, from the purest silvery white 
through light green, rosy pink, and creamy or golden 
yellow, to a shimmering black. Pearl thus serves most 
effectively as a foil for the bright reflection and intense 
fire of diamond and as a frame to enhance almost any 
kind of gem. As a row of individual gems, however, 
pearl is most highly regarded, for its beauty is sufficient in 
itself. For a gem of symmetrically spherical outline, 
translucent, with a rich but subdued sheen, and free from 
blemishes, "pearl of great price" has literal significance. 

Pearl is a gem but not a gemstone. It is formed within 
the interior of certain inollusks which secrete the pearl- 
substance to line the shells in which they live. These mol- 
lusks, or shellfishes, are invertebrate animals which remove 
calcium carbonate from the water and with it build their 
shells. Inside the shell, enveloping the soft parts of the 
body, is a mantle which has cells that secrete both organic 
and mineral matter. The organic product of the mantle 
is .called conchiolin, a brown substance related to the chitin 
of which our fingernails are made. The mineral product, 
derived from the sea, consists mainly of two crystalline 
forms of calcium carbonate, calcite (hexagonal) and arag- 
onite (orthorhombic). 


The shell is constructed in three layers, growing con- 
tinuously and at the same time, but secreted in a regular 
order. The outer layer, deposited first, consists of con- 
chiolin; the middlp layer consists of tiny prisms of calcite 
cemented with conchiolin, and the inner layer consists of 
overlapping flakes of aragonite also cemented with con- 
chiolin. This last layer is iridescent and is known as nacre 
or ?ttother-of-pearl; as an ornamental material for buttons, 
implement handles, and inlaying it is well known. 

The immediate cause of pearl formation is an irritation, 
resulting from disease or the introduction of a parasite or a 
foreign particle such as a grain of sand or piece of broken 
shell. To allay the discomfort the mollusk, through its 
mantle, secretes its customary products to seal off the in- 
trusion. These products are built up in concentric layers 
like an onion, in reverse order from the arrangement in the 
shell the zone of conchiolin being deposited first around 
the uninvited object and later surrounded by the two 
mineral zones to complete the pearl. The outer surface 
of pearl therefore corresponds to the mother-of-pearl layer 
of the shell. 

To assume the ideal round form, a pearl must, of course, 
have been loosely held among the soft parts, the tissue or 
muscles, of the mollusk. If, however, a boring parasite 
has penetrated beyond the mantle and into the shell of 
the animal, nacreous material is deposited at that spot, and 
an irregular hollow pearl, known as a blister pearl, is 
formed. A solid pearl of any irregular shape is called 
a baroque pearl and may have been produced by the depo- 
sition of nacreous material against a fragment of some 
rough object, such as a bit of wood, or by other means 
unfavorable to symmetrical growth. A pearl may become 


attached to the inside of the shell, in which case the pearly 
substance deposits only on the outer half, furnishing a 
hemisphere rounded on one side and flat on the other; 
such a gem is called a button pearl and i^ suitable for rings 
where only half of the pearl shows. Since a pearl may 
grow into almost any shape, many fanciful names are used 
in the trade. Round and pear-shaped pearls command the 
highest prices. Seed pearls are round ones weighing less 
than a quarter of a pearl-grain, and dust pearls are the most 
minute in size. 

The texture of pearl is called its skin, and the luster is 
called its orient. Orient is due to the combined optical 
effects of interference of light from the thin curved layers 
near the surface and diffraction of light from the flaky 
layers of nacre that overlap one another. The rich orient, 
necessary to a valuable pearl, may be lacking when too 
much conchiolin is present. Traces of impurities in the 
water affect the color of pearl, and varying amounts of 
conchiolin give it a yellow to brown hue. 

Of all gems, pearl is particularly susceptible to deteriora- 
tion. The conchiolin, because it is organic, decays after a 
century or two. The calcium carbonate is immediately 
attacked by acids, even by perspiration. The moisture 
content gradually decreases in warm, dry climates, and a 
certain porosity allows for the absorption of grease and 
oil: Pearl, moreover, is not hard. Once scratched or 
stained, pearl cannot be permanently improved except by 
the uncertain procedure of peeling off the outer layers 
with a sharp blade. 

Familiar enough is the newspaper story about the finding 
of a pearl in a restaurant oyster. It is true that the edible 
oyster does on occasion produce pearls, but the quality is 


rarely good (especially after being cooked!) or the value 
more than nominal. The really precious pearl comes from 
various mollusks belonging to the same class but different 
genera. The shells may be single (univalve) or in pairs 
(bivalve). Two major types of pearl-bearing mollusks are 
recognized, according to whether they live in the ocean or 
in rivers. The salt-water pearl comes from the pearl 
oyster, whereas the fresh-water pearl comes from the 
pearl mussel. The pearl oyster includes a number of 
species of the genus Meleagrina, which provides the finest 
pearls and the best mother-of-pearl. Fresh-water pearls 
from inland streams are produced by mollusks of the genera 
Unio and Anodonta. In addition to these, other mollusks, 
including the clam, conch, and abalone, produce pearls. 

Pearl fisheries encircle the globe. The product of each 
region is usually characterized by distinctive color, shape, 
or size that to an expert identifies the locality. Some spe- 
cies of mollusks are restricted to certain places but others 
are widely distributed. The unhappy experience which 
led the pearl mollusk to create in self-defense so wondrous 
an object is revealed in the distorted and stunted appear- 
ance of its shell. Such abnormal shells are eagerly sought 
and swiftly gathered in baskets by the divers, who remain 
about one minute at each descent. 

The Arabian coast of the Persian Gulf has been a lead- 
ing fishery since the Macedonians worked its oyster beds 
over 2,000 years ago. Another source of pearl for the 
ancients, in the Gulf of Mannar off the northwest shore 
of Ceylon, is also still important. The fisheries of the 
northern and western shores of Australia are noted, not 
only for their yield of pearl and mother-of-pearl, but also 
for the modern methods that are employed, including the 


use of diving suits. Other productive localities are the 
Sulu Sea northeast of Borneo; the shores of the Aru Islands 
southwest of New Guinea; the lagoons and outer waters of 
scattered South Pacific coral islands and atolls; the Gulf 
of Mexico, the Caribbean Sea, and the western coast of 
Central and South America. 

River pearls are taken from streams in several parts of 
Europe and America and in China and Japan. The most 
famous are those from Scotland, Wales, and Ireland, but 
by far the most productive fisheries are in the Mississippi 
and its tributaries, where systematic collecting has been 
done on a small scale each summer for many years. 

The pearls found in Chinese river mussels furnished the 
inspiration for the experiments in artificially inducing pearl 
growth that led, seven centuries later, to the production of 
the cultured pearl, described in the chapter on u Man-Made 


When coral is considered an animal skeleton for such it 
is its romantic appeal may be regarded skeptically. Never- 
theless, precious red or pink coral has been highly prized 
as a gem since ancient times and still is thought of as having 
a loveliness of its own, not dazzling or glowing, but quietly 
pleasing. In remote parts of the earth coral constitutes a 
source of wealth and is used for ornamenting clothing, 
jewelry, and valued articles of many kinds. Although 
found chiefly in the Mediterranean, coral was so much in 
demand in India during Roman days that there was little 
left for the inhabitants of the places that produced it. Good 
specimens of red color were widely used in China for the 
hat buttons that distinguished mandarins from other public 


officials. Coral contrasts so well with the blue and green 
hues of turquoise that in the mountainous parts of central 
Asia the two gems are worn together. At present coral is 
most popular in Italy, where the people have a near- 
monopoly of the fisheries and the manufacturing, turning 
the newly found coral into beads and sundry decorative 
Items, often of curious shapes. 

Fig. 101 Corals 

A, modern coral colony, showing relation of living polyps (a-d) 
to stony skeleton (e). #, common type of ancient coral. [From Schu- 
chert and Dunbar Textbook of Geology, 4th edition, copyright 1941. J 

Only an excessively small part of the world's coral can 
be classed as gem material. Common coral of the reef- 
forming type covers vast areas of the warm oceans, and 
fossil coral is distributed in many regions where the climate 
in past geologic ages was favorable. Coral is created by 
tiny marine animals called polyps, which live in branching 
colonies (Fig. 101) that gradually extend themselves in 
size as new polyps grow. These organisms remove calcium 
carbonate from the water, deposit it in their tissues as 
crystallized calcite, and use it to build their skeletons, 


which they leave to accumulate when they die. Impuri- 
ties in the mineral matter give coral its color. 

Gem coral is dredged mostly from shallow waters but 
may be found in depths to 1,000 feet. Besides the borders 
of the Mediterranean and around the larger islands, precious 
coral is secured in the Atlantic Ocean off Africa and Ire- 
land, in the Pacific Ocean off Japan and Australia, and 
in the Persian Gulf. From the two latter seas the unusual 
black coral is obtained. 


Ancient in its use as a gem and even more in its origin, 
amber occupies an eminent place in gemology. There is 
no such thing as "new" amber. All of it began 10 million 
or more years ago, in what geologists call the Tertiary 
Period, when extensive forests of conifers grew along the 
Baltic coast in a warm climate very unlike that of the 
present day. Amber is the yellow resin now hardened 
and fossilized into irregular lumps that oozed from one 
species of tree, a pine called Pimis succhiifera. The drops 
of resin remained on the ground while the trees decayed 
and were covered by invading seas; the forests were then 
buried by later sediments which incorporated the amber 
reworked from the previous deposits. The great glaciers 
of. the Ice Age subsequently ploughed through this region, 
distributing some of the amber southward. Even now the 
Baltic Sea beating on the shore plucks loose the weakly 
consolidated rock and claims the amber in it for its own. 
Pieces are washed up on coasts as distant as England. 

From these soft beds, called blue earth, comes the bulk 
of the world's amber. Until a century ago amber was 


gathered from among seaweed at low tide. It has since 
been recovered in large quantities by open-pit mining. 
The center of production is on the peninsula of Samland 
in East Prussia, northwest of Konigsberg. 

Amber from northern Europe was marketed by the 
Phoenicians, who made it known to all the Mediterranean 
nations. Elaborate trade routes have traced the distribu- 
tion of Baltic amber, which was the principal article of 
commerce between northern and southern Europe when 
amber beads served as a medium of exchange. 

One of the most significant properties of amber, its 
ability to become negatively electrified by friction and to 
pick up tiny bits of various materials after being rubbed, 
was well known to the Greeks; from their name for the 
substance, elektron, is derived our word electricity. The 
word amber itself is Arabic. 

Even more interesting than its electrical nonconductivity 
is the presence in many pieces of amber of a fascinating 
exhibit of entombed insects. As the sticky fluid exuded 
from the trees, it ran down the bark and caught within its 
fatal grasp any creature attracted to its sweet odor and 
any light object blown against it by the wind, and these 
were covered by the next flow of resin. Hundreds of 
kinds of insects spiders, flies, beetles, ants, and centipedes 
and equally varied plant remains have been preserved 
with extraordinary fidelity, even to the tiniest antenna or 
finest cell pattern. (See Fig. 102.) As may be expected, 
some of the insects are only slightly different from those 
that plague us today, whereas others have become extinct. 
Much light is thrown on the fauna and flora of early times. 
Not only organic substances but almost any material con- 


taminated the purity of amber. Alexander Pope wrote in 
An Epistle to Dr. Arbuthnot: 

"Pretty! in amber to observe the forms 
Of hairs, or straws, or dirt, or grubs, or worms! 
The things we know are neither rich nor rare, 
But wonder how the devil they got there." 

Amber of all hues of yellow, ranging from almost color- 
less to almost black, has long been carved into a multi- 
plicity of ornamental articles. Beads, pipestems, and ciga- 
rette holders are especially familiar. Prized in the art 
collections of large museums are wonderfully executed 
amber objects such as jewel cases, complete chess sets, 
carved screens, statuettes, altars, and shrines. 

Amber from the Baltic coast is properly referred to by 
its mineralogical name, succinite. It is a hydrocarbon, 
composed of hydrogen, oxygen, and carbon in variable 
proportions, and represents a mixture of succinic acid, 
several different resins, and a brown volatile oil called 
amber oil. When boiled, amber deposits a black substance 
called colophony or amber pitch, which is the principal 
ingredient in the production of amber varnish. 

There are several other varieties of amber differing 
somewhat in composition from succinite. They are named 
according to the locality from which they come. 

'Sicilian amber or siinetite is the choicest and rarest, for 
its yellow color may be tinged with a glorious red and 
highlighted by a blue or green fluorescence that gives it 
some of the beauty of opal. The gem, furthermore, is 
usually clear and transparent, because it lacks the great 
number of bubbles that so often make Baltic amber cloudy 
and almost opaque. 


Rumanian amber or rnmanite is less well known than 
the others. It is characterized by many cracks and open 
spaces that give a curious glistening effect. 

Burmese amber or burmite contains little or no succinic 
acid, as it belongs to the reunite group of resins, It conies 

Yale Peabody Museum. 

Fig. 102 Insects Preserved in Baltic Amber 

Enlarged views showing the delicate detail, [From Schuchert and 
Dunbar Textbook of Geology, 4th edition, copyright 1941.1 

from the Myitkyina district in Burma which also fur- 
nishes jadeite and is mined in primitive fashion and shipped 
mainly to China. Cracks filled with calcite too frequently 
mar the clarity of burmite. 

As may be inferred from its recovery from the sea, 
amber is light enough to float in salt water; by this simple 
means it may be distinguished from glass and plastics (such 
as bakelite), which are the most common imitations. 
Amber is slightly too hard to be scratched by the finger- 
nail, but it can be carved easily with a knife, drilled, and 
worked on a lathe. Amber is entirely amorphous, having 


no crystal form or crystalline character. It will burn in 
a match or candle flame and gives off white fumes and an 
aromatic odor; the German name for amber, bernstein, 
means "stone that burns/' 

Because amber softens at a low temperature, small 
fragments of it are artificially compressed to form ambroid 
or pressed amber, which is then handled in the same way 
as the original material or extruded in the shape of rods. 
This product can scarcely be called an imitation but may 
be considered reconstructed amber. 

Other natural resins besides amber serve similar pur- 
poses. Copal is a fossil resin, though younger than amber, 
and comes mainly from Africa; kauri gum is a modern 
resin from New Zealand. Chemical tests are needed to 
differentiate between them and true amber. 

Ambergris, the name of which is the source of the word 
amber, is in no way related to amber. Ambergris is a fatty 
concretion formed in the body of whales and found float- 
ing in the sea; it is used in perfumery. 


Although, like amber, it owes its origin to tree life, jet 
nevertheless has had a very different history, because the 
wood itself, rather than the resin, has been preserved and 
is' used in jewelry. Jet is a black variety of lignite, a rank 
of coal intermediate between peat and anthracite. It is 
derived from ancient coniferous wood through compac- 
tion and decomposition. The choicest quality of jet is uni- 
form in color and in texture, dense enough to take a lustrous 
polish like black velvet and tough enough to be turned 


on a lathe or carved with a knife. It has a conchoidal or 
shell-like surface when it is broken. 

Small ornaments of jet have been recovered from caves 
of prehistoric peoples in several parts of Europe, and jet 
amulets have been found in Indian pueblos in the Ameri- 
can Southwest. The chief places, however, that are iden- 
tified with this material are England and Spain. Spanish 
jet is imported into England to help maintain an industry 
that antedates the Roman occupation. Bronze-age buttons, 
rings, and beads have been found in pits throughout the 
country. British jet is often referred to as Whitby jet 
from the town on the Yorkshire coast that serves as the 
center of mining and craftsmanship. Early residents of 
the monastery of Whitby Abbey had rosary beads and 
crosses made from the jet found in the vicinity. 

The so-called jet rock near Whitby is a shale containing 
logs and irregular pieces of jet associated with fish scales 
as evidence that this land was once submerged by the sea. 
Loose fragments of jet broken off by the waves and washed 
back onto the shore were for a long time the only source 
of supply, but eventually it became necessary to dig pits 
and mines into the rock itself. 

Jet is utilized chiefly for religious articles and mourning 
jewelry, which was more fashionable during the 19th cen- 
tury than now. 

Although the derivation is obscure, the word jet comes 
from a place in Asia Minor called Gagas where it was first 


Chapter 7 

Man-Made Gems 

Imitation seems to be one of the universal traits of the 
human race. The cave man probably amused himself be- 
tween bear hunts by grunting and growling in the manner 
of his prey. When he had progressed to the state in which 
he attached a high value to inanimate things of beauty, he 
tried to prepare substitutes for them to make them more 

The Egyptians were skillful in the manufacture of gems 
from various materials and their achievements may be 
seen in museum collections of ancient art. The Romans 
reproduced their favorite gem, pearl, in enormous quanti- 
ties. Later fine glass imitations called paste became so 
popular in Europe that they were a fad among the wealthy. 
All these substitutes are rather easy to identify, as their 
appearance is the only similarity between them and natural 

Through the magic of modern chemistry, much more 
amazing gemstones are available in a fascinating array of 
colors at the nearest jewelry store. So faithful in appear- 
ance and perfect in form are these synthetic stones that 
only an expert can recognize them with certainty; indeed, 


their very size and perfection are often the surest clues to 
their origin, for they rival the famous gems of history, 
the treasures of emperors and queens and merchant princes. 

In addition to genuine gems those which are formed in 
the earth or sea by the processes of nature or which come 
from beyond our world the gem kingdom includes five 
types of artificial gems. These may be classified as imita- 
tion, synthetic, composite, treated, and cultured. 

An imitation gem is a substance which is wholly manu- 
factured but contains no natural gem material, even though 
it is made to look like a real stone. A synthetic gem is 
entirely different because it is crystalline and has every 
property of the natural gem; it is distinguishable only by 
certain minor peculiarities of structure due to the mode of 
manufacture. A composite gem consists of several pieces 
assembled to make a single larger or seemingly more 
valuable stone; even if it often serves a useful purpose by 
providing increased surface hardness, its primary intent is 
generally to deceive. A treated gem is one the natural, 
original color of which has been improved in salability by 
the application of heat, chemicals, or radioactivity. A 
cultured gem is a pearl grown by man's deliberate inter- 
vention in the life of an oyster. In the discussion of man- 
made gems, too rigid an adherence to an arbitrary classi- 
fication may bring needless confusion, because there are 
so many intermediate kinds and so many possible combina- 
tions. The chief characteristics of these five main types, 
however, will be described in this chapter. 



A considerable number of minerals, including many of 
the gems, have been made synthetically in the laboratory. 
They have the same chemical composition as the natural 
minerals and are essentially the same in all other respects 
except their origin. Only the few that have an important 
industrial use are made commercially. 

Though they may be made in almost every conceivable 
hue and nearly every possible shade and tint, all the syn- 
thetic gems are varieties of only three species corundum, 
spinel, and beryl. The flaming red ruby and the celestial 
blue sapphire are the best-known members of the corundum 
family. Spinel, on the other hand, is rather an unfamiliar 
stone, rather similar to corundum; there are natural crystals 
of both in the same gem gravels of the Orient, and until 
recently distinction was seldom made between them. A 
large proportion of the unusual gem names that one en- 
counters are really trade-marked names for either synthetic 
corundum or synthetic spinel. Dirigem, erinide, ultralite, 
emerada, rozircon, and others often sold as new genuine 
gems are varieties of one or the other. Some colors are 
more conveniently made in corundum and others in spinel. 
Ruby and sapphire being natural varieties of corundum are, 
of course, reproduced synthetically in that species. Syn- 
thetic beryl is as yet represented only by its choicest va- 
riety, the green emerald. 

Reconstructed Gems 

No gems were known to be made synthetically until 
about sixty years ago, when a jeweler became suspicious of 


some rubies that he had bought; upon examination he saw 
that they were unlike any others in his stock. They were 
traced to an obscure chemist in Geneva, Switzerland, who 
had made them by fusing together several small rubies at 
a high temperature. In spite of their bubbles and cracks, 
their odd shade of color, and their brittleness, these stones 
were an improvement over all previous artificial gems, and 
somewhat better ones that were made afterward secured a 
ready sale. 

For this type alone the term reconstructed should be 
reserved. The word is still erroneously applied to modern 
synthetics, but should be used only for the gems that re- 
sulted from the fusion of actual rubies. No "reconstructed 
sapphire" has ever been produced, for the blue color does 
not persist under the required amount of heat. 

Pressed ainber^ which consists of small fragments of 
amber fused into a plastic mass, may also, as far as origin 
is concerned, be regarded as a reconstructed gem. 

Synthetic Corundum 

If bits of stone could be made into a single piece by arti- 
ficial means, why, it was reasoned, could not such gems be 
made more cheaply by combining directly the simple 
chemicals of which they are composed? So scientists took 
up the challenge and set to work to prepare in a laboratory 
the rare gems that required long ages to form within the 

Edrnond Fremy, a French chemist, in collaboration with 
Charles Feil, was finally able in 1877 to produce some ruby 
crystals, but they were too small to be of much value and 
hardly better than the tiny flakes made by Marc Gaudin 


as early as 1837 or the small colorless fragments made by 
Ebelman in 1847. When Fremy had to retire, his able 
young assistant, Auguste Verneuil, took up the problem. 
With a perseverance that refused to recognize failure he 
invented new equipment and devised new methods. Suc- 
cess was achieved in 1902, with the production of syn- 
thetic ruby of admirable beauty, perfection, and size. 

Synthetic sapphire was produced in 1910, only after the 
elusive blue color had first been secured accidentally in 
an entirely different species, which was discovered to be 
spinel. Since then synthetics have been put on the market 
in a wide array of colors, and the end has not yet been 
reached. The outstanding recent accomplishment is the 
introduction by the Linde Air Products Company of star 
ruby and star sapphire, which were made available in com- 
mercial quantity in September 1947. 

VerneuiPs method is still used in the manufacture of the 
millions of carats of synthetic corundum and spinel that 
are made every year. The equipment, only slightly modi- 
fied from the original for more economical operation, is 
shown in Fig. 103. It is in general an inverted blowpipe 
which creates a high-temperature flame by a mixture of 
oxygen and hydrogen. Aluminum oxide powder, ground 
to particles the size of 4-millionths of an inch and mixed 
with the proper coloring matter, is fed through a screen by 
earn action and drifts down a tube of oxygen. Meanwhile, 
a jet of hydrogen enters from the side, and at the point at 
which the two gases meet, a flame of over 3,750 degrees 
Fahrenheit is obtained. The powder melts and drops onto 
a rotating pedestal as a single pear-shaped crystal called a 
boule, several stages in the growth of which are shown in 
Fig. 104. Its sides are smooth and bright, whereas its top 

' 250 

is usually irregular and represents an abortive attempt to 
form the hexagonal crystal faces typical of corundum. 
After cooling, it is removed from the furnace and split 

Fig. 103 Verneuil Furnace for Manufacture of Synthetic 


[Linde Air Products Co.] 

lengthwise to ease the strain that seems to he present. 
Boules average several hundred carats in weight. They 
are cut by the same methods as genuine gems. 

A colorless stone, called synthetic white sapphire, is 
made from pure aluminum oxide, free from the impurities 


that tend to darken it. As in the natural stone, chromium 
oxide is the coloring matter in synthetic ruby. A smaller 
amount of chromium gives the tint of pink sapphire. Ti- 
tanium oxide causes the blue color of synthetic sapphire. 
Nickel oxide imparts a range of yellow colors. The orange 

Fig. 104 Boules of Synthetic Corundum 

[Linde Air Products Co.l 

variety called padparadschah is seldom seen in natural 
corundum. A most unusual kind, colored by vanadium 
oxide, is wrongly called "synthetic alexandrite" because 
its color changes from green in daylight to red at night, 
as in the real gem, though the contrast of color is not 
nearly as distinct. It could not be synthetic alexandrite 
for it does not possess, except in appearance, the properties 
of chrysoberyl, of which true alexandrite is a variety. 
The addition of other metals to the vanadium yields other 
hues of green. Chromium and iron added to the titanium 


of blue synthetic sapphire give a violet color. There is 
no commercial synthetic zircon or synthetic aquamarine, 
only synthetic corundum or synthetic spinel made in col- 
ors that are more or less appropriate. 

These synthetic stones resemble the older imitations only 
in that both are man made. Otherwise they are so much 
like Nature's own gems that only a trained eye aided by a 
strong magnifying glass, sometimes even by a microscope, 
can determine which is the natural stone and which the 
manufactured one. They are alike in all important re- 
spectshardness, specific gravity, refractive index, disper- 
sion, and other properties which identify a gem. X-ray 
pictures show th^ structures to be precisely the same. 

It happens, however, that the very process of making 
a synthetic stone leaves its "fingerprints," and the gem de- 
tective looks for these clues. The internal markings- 
bands of color and lines of structure which are due to 
slightly variable conditions during growth are curved in 
synthetics, instead of being straight and angular as in 
genuine corundum. Synthetics contain round and oval gas 
bubbles, whereas the inclusions in genuine stones consist 
of actual crystals (as needles and in other shapes) of the 
minerals that occur in the earth with ruby and sapphire, 
and these inclusions have regular sides or intersect at ex- 
actly 60-degree angles. The kind and quality of the stone 
determines whether these intimate marks can be found 
with a hand lens or require a microscope. The bands of 
color in blue synthetic sapphire, for example, are more 
conspicuous than in the other varieties. 

Because it is easier to cut synthetic-ruby boules without 
attempting to orient them, as is carefully done with most 
genuine rubies, the optic axis the direction of single re- 


fraction may lie in any position within the stojie. Not 
only is the resulting color somewhat anomalous in com- 
parison with that of a real ruby, but the twin dichroic 
colors of a synthetic are usually visible *when a dichro- 
scope is held against the top or table facet, whereas natural 


105 New Rod Form of Synthetic Corundum 

[Linde Air Products Co.] 

ruby appears best when the table is perpendicular to the 
optic axis. 

Apart from its use in jewelry, synthetic corundum plays 
a vital role in modern industry. Originally developed for 
instrument bearings, especially in watches and meters, it 
acquired new significance during the war, when an expand- 
ing technology found it valuable in equipment such as va- 
cuum thermionic devices, diesel-engine injection nozzles, 
thread guides, oil-burner nozzles, and special abrasives. An 
entirely new use, which promises much for the future, is 
for gauges. A strand of nylon has recently been found to 


be the most effective 'polishing agent for the synthetic- 
corundum bearings in naval precision instruments, such as 
range finders. 

When shipments from Switzerland, France, and Ger- 
many were threatened by the war, the Linde Air Prod- 
ucts Company undertook in the autumn of 1940 to make 
synthetic corundum in the United States. Their factory 
opened in April 1942, and they claim to have made this 
country forever independent of foreign supplies. Another 
major triumph,,, previously attempted for 40 years in 
Europe without success, has been the manufacture of a 
new cryst^ form to supersede the familiar boule that is 
made for gems. By producing the corundum in long 
slender rods, shown in Fig. 105, several steps can be 
eliminated in the preparation of bearings. The boules 
must be split lengthwise to relieve stresses but the rods are 
annealed. Most of the material for industrial purposes is 
confined to the colorless variety, known in gemology as 
synthetic white sapphire. 

Synthetic Spinel 

In an attempt to secure a more even distribution of the 
difficult blue color in synthetic corundum, magnesium ox- 
ide was added as a flux. The resulting stone proved to be 
a different species, corresponding in composition to spinel. 
<The boules, with square cross-section, show a more dis- 
tinct crystal form than those of synthetic corundum, and 
they are isometric instead of hexagonal. 

The most unusual feature about the composition of syn- 
thetic spinel is its excess of aluminum oxide. Most of the 
gems seem to have two or three times as much as is required 


by the chemical formula, and thus they begin to approach 
the composition of corundum. This has its effect on the 
specific gravity and refractive index, which are thereby 
increased, although they seem to stay within the known 
range of natural spinel. 

The blue stones are the most popular; those made to 
substitute for zircon and aquamarine are colored with 
cobalt oxide, as are those of the brilliant blue color that 
are sold simply as blue spinel, though their hue is quite 
unlike any natural spinel. A variety resembling alex- 
andrite is produced, as in synthetic corundum, but the 
agents responsible for the peculiar changing color are 
chromium and cobalt, rather than vanadium. Synthetic 
spinel of many other colors, as well as colorless stones, 
are also made to satisfy the demands of the jewelry trade. 

The internal structure of synthetic spinel is much clearer 
than that of its corundum counterpart and seldom shows 
either curved striations or gas bubbles. 

Until World War II synthetic spinel was not used in- 
dustrially except for gem purposes because its hardness, 
although considerable, is inferior to that of corundum, 
which costs no more to manufacture though more to cut. 
German wartime research, revealed in 1947 by the Office 
of Technical Services, succeeded in developing a process 
whereby synthetic spinel, after being cut into jewels for 
bearings, was hardened by heating. 

Synthetic Beryl 

To these two commercial species of synthetic gems, 
corundum and spinel, can now be added a third beryl. 
Its wonderful emerald variety, since early times one of the 


most highly prized of all the gems, is now on the market 
in synthetic form, though still in small sizes. 

Owing to the complexity of its chemical composition, 
in contrast to the much simpler corundum, attempts to 
synthesize emerald, or even to reconstruct it by fusing 
together pieces of actual beryl, had been attended by re- 
peated failures. The result was always green glass instead 
of the required crystalline material. About 1934 two 
German chemists finally succeeded, though not by the 
Verneuil process, in making synthetic green beryl, to which 
they gave the name igwerald. In addition to having dis- 
tinctive wisplike internal markings, it differed from most 
natural emerald in fluorescing red under ultraviolet light. 
Improved American gems, not yet over 1 % carats in weight, 
have since become available, and future advances in manu- 
facture seem likely to put synthetic emerald on a basis 
equal to synthetic ruby and sapphire in size and color. 
Prices are still high and the color does not equal that of 
the best natural emeralds but is better than the average. 

Apart from their frequent fluorescence, the best means 
of identifying synthetic emerald is to observe the inclusions 
under high magnification. The black inclusions in the 
synthetics appear green, showing that they are a concen- 
tration of the coloring matter, which is chromium oxide, 
rather than the liquid bubbles found in genuine emeralds. 
Real emeralds, furthermore, contain carbon spots and tiny 
crystals of foreign minerals which are never present in 
synthetic stones. 

The question is often asked why anyone would spend 
hundreds or thousands of dollars for a natural gem, when 
for a small part of that amount he can buy a stone which 


will deceive everyone except an expert. The answer is 
that much of the price of a real ruby or emerald lies in its 
rarity, and people will continue to pay the large sums that 
rare and beautiful things always command. 

"Synthetic Diamond" 

A lively interest has been maintained for a long while in 
the possibility of making synthetic diamonds. Apart from 
the prospect of drastic readjustments that might be faced 
by the jewelry business and the even more extensive bene- 
fits that should accrue to industry in general from an un- 
limited supply of its best abrasive, the remarkable optical, 
physical, and chemical properties of diamond would in 
themselves make its synthesis an achievement of extraor- 
dinary significance. To produce in a laboratory what is 
probably the most noteworthy substance of the inorganic 
world would indeed be a triumph of science. 

All the older books on gems state that very small dia- 
monds were made by Henri Moissan, a 1906 Nobel prize 
winner. His experiments were believed to have been suc- 
cessful, even though obviously not to a commercial extent. 
Carbon, which was obtained by burning sugar, was dis- 
solved in molten iron, and upon being cooled quickly the 
metal exerted a tremendous internal pressure. The tiny 
particles that crystallized were assumed to be diamonds, 
but newer tests indicate that they were a carbide rather than 
a form of carbon. Other methods have been tried for many 
years by a number of competent workers, including several 
of the most distinguished scientists of recent times. Ger- 
man experts carried on extensive research during the war, 


repeating Moissan's experiments and always with failure. 

Diamond is deceivingly simple. In composition it is the 
only gem consisting of just one chemical element, carbon; 
it nevertheless defies the artificial reproduction of its single 
constituent. Carbon presents the difficulty of burning into 
a gas before it melts into a liquid. When it does crystal- 
lize, it is more likely to do so as its more stable form, the 
mineral graphite. 

Most investigators have assumed that great pressure was 
the key to the production of diamond, and their equip- 
ment was designed chiefly to create it. An observation by 
Dr. Nininger, who found diamond crystals in a meteorite 
next to a cavity which could hardly have existed under 
much pressure, casts considerable doubt on the theory. 
Experiments described in 1947 by Percy W. Bridgman, 
who was awarded a Nobel prize in physics for his work 
with extremely high pressures, indicate furthermore that 
high pressure alone is ineffectual in making synthetic 


Gilbert and Sullivan's Learned Judge, who wore "a ring 
that looked like a ruby," wasn't fooling himself, however 
much he might deceive others. He knew that the only 
similarity was a bright red color. All imitation gems re- 
semble genuine ones solely in their superficial appearance, 
and, unlike synthetics, they may, be identified with cer- 
tainty by determining their optical or other physical prop- 
erties. Although conspicuously inferior to synthetics in 
hardness, imitation stones frequently are as hard as some 
of the genuine stones which they are supposed to repre- 


sent. Their chief advantage over synthetics lies in their 
even greater variety of color. Apart from the small syn- 
thetic beryl that is beginning to come into the market, 
the rich green of emerald, for example, can be obtained 
in no other homogeneous material, natural or otherwise, 
except glass. Some gems, particularly those showing curi- 
ous optical effects, like opal and moonstone, cannot be 
made synthetically. The low cost of imitation gems is 
another advantage, for they are much less expensive to 
manufacture than synthetic crystals, and, before being 
polished, they are merely molded instead of cut. 

Most imitation gems are made of glass. This versatile 
substance has been known for thousands of years, yet it 
is just entering upon its most promising era. Two main 
kinds of glass, crown and flint, are used for gems. Both 
consist mostly of silica obtained from sand; crown glass 
also contains calcium oxide (lime), and flint glass contains 
lead oxide. Metallic oxides and other chemicals are added 
to produce almost any desired shade or tint. Nontranspar- 
ent glass, such as is used for imitations of opal and opaque 
gems, requires somewhat further treatment. 

Because the ingredients may be mixed in almost any 
proportions, glass has a wide range of properties, though 
the types used for gems are fairly restricted. In rare cases 
glass may, usually by coincidence, have the same refractive 
ifidex or specific gravity as a genuine gem of the same 
color. Two especially pure and constant kinds of glass 
are fused quartz (vitreous silica) and beryl glass, both of 
which are made by fusing the natural minerals into an 
amorphous mass; the chemical composition remains the 
same but the properties are changed. 


Jewelers refer to the common glass imitations as paste, 
and the same material appears in the costume-jewelry 
advertisements of department stores under the term "simu- 
lated." A brilliant lead glass used to imitate diamond is 
called strass. A most distinctive and attractive gem is 
goldstone, made of copper filings in glass. Imitation gems, 
as well as genuine ones, are often improved in brilliancy 
or color by foils, usually of metal, placed on their lower 
facets, or by coatings of mercury or pigment. Rhinestones 
and so-called brilliants are of this kind. Glass gems, being 
noncrystalline, may be distinguished from many genuine 
stones by their lack of double refraction and complete 
absence of dichroism, as well as by the presence of air 
bubbles and a measurable difference in properties. 

Formerly concentrated almost exclusively in Czecho- 
slovakia, the manufacture of glass imitations was intro- 
duced into the United States when imports from the occu- 
pied countries were halted during World War II. This 
infant American industry is at present struggling against 
the threat of cheap foreign competition. The molten 
glass, combined according to formula, with coloring mat- 
ter added, is drawn into long rods called canes; one end 
of a cane is melted into a die of the desired shape. The 
better-quality stones are later polished. Hard glass is being 
developed that offers good prospects for the gem industry 
of the future. 

Another imitation gem material, much more modern 
than glass but already useful in countless ways, comprises 
the group called the plastics. These are marketed under a 
variety of names, from the original celluloid to the familiar 
Bakelite and Catalin. Amber and jet, the two lightest 
gems, are imitated with particular effectiveness in plastics, 


which like them have a resinous luster and a low specific 
gravity. Natural amber, however, is even lighter in weight 
than its man-made substitutes. 

Other materials are used to a lesser extent. Imitation 
turquoise is commonly made from porcelain and sometimes 
from enamel or bone. Ornamental stones may be imi- 
tated in plaster. Stainless steel containing chromium and 
nickel was rather widely sold a few years ago as "scientific 
hematite." The warrior-head intaglio design is stamped 
into the metal, producing a smoothly curved surface unlike 
the sharp lines of a hand-carved stone, and the character- 
istic red streak of true hematite is absent. Another im- 
portant substitute for hematite is made of a ceramic 

The best-quality imitation pearl dates back to 1656, 
when a Frenchman coated the inner side of a hollow sphere 
of opalescent glass with parchment sizing and applied to 
this sizing a preparation made from fish scales and called 
pearl essence. The rest of the interior was then filled with 
hot wax. This type of pearl is harder than the natural 
gem and of course has a glassy texture. 

The average imitation pearl produced now, however, 
consists of a glass or plastic bead coated on the outside 
with pearl essence. The tendency of this material to peel 
is. usually visible at the drill-hole. 

A current post-war boom has developed among the Bay 
of Fundy fishermen, who find their catches of young her- 
ring worth far more for the silvery fish scales used in the 
manufacture of pearl essence than for food. Four fac- 
tories are now operating in Maine and two more are due 
to open soon in Canada. 



Two or more pieces assembled to make a single indi- 
vidual constitute a composite gem. Doublets (Figs. 106 and 
108) contain two pieces and triplets (Figs. 107 and 109) 
contain three. These may be cemented or fused together, 
either before or after the cutting process. Composite gems 


Colored glass 

Fig. 106 
Part-Garnet Doublet 

Fig. 107 
Part-Garnet Triplet 



Green glass 

Fig. 108 Diamond Doublet Fig. 109 Soude Emerald 
Composite Gems 

may consist entirely of genuine stones, or of a combina- 
tion of real and imitation materials. (All-glass composites, 
or glass with a foil back, can hardly be classed as anything 
but imitations.) Except the opal doublet and emerald 
triplet, composite gems are seldom made these days. 

Older jewelry, however, contains them in abundance. 
They were originally designed to pass the hardness test, 


first by the addition of a hard top of a natural mineral, 
usually quartz or almandite garnet (Fig. 106), and later by 
similar protection of the bottom (Fig. 107). The devel- 
opment of synthetic corundum and spinel, with their su- 
perior hardness and wide choice of color, has made this 
arrangement unnecessary. 

When the purpose is to combine several fragments of a 
genuine gem into one larger and consequently more valu- 
able stone, only the natural material is used. Diamond 
doublets (Fig. 108) are on rare occasions made in this 

A familiar doublet involving precious black opal derives 
its value from the tendency of this exquisite gem to occur 
in layers of such thinness that they need to be supported 
in order to be mounted in jewelry. By cementing the opal 
slice onto a base of ordinary black opal or black chal- 
cedony, the necessary strength is secured. 

The most successful substitute for emerald is a triplet 
called soude emerald (Fig. 109), consisting of a top and a 
base of quartz, enclosing between them, sandwich-like, a 
flat plate of green glass which furnishes the color. The 
quartz assures a reasonable degree of hardness and may 
show natural flaws resembling those of emerald. This 
substitute is important because the rich color of emerald 
has never been produced in synthetic corundum or spinel, 
with their superior durability, and synthetic beryl is made 
only in small specimens which have not yet entered the 
market in quantity. 

The true nature of a composite gem becomes evident 
when the surface separating the parts can be seen. Be- 
cause all stones assume the color of their back facets, any 
difference in color between the sections is visible when a 


gem is viewed sideways. Holding it over white paper or 
cloth and breathing upon it helps to reveal the plane of 
junction. The best way, especially when a stone has a 
uniform color throughout, is to immerse it in a highly 
refractive liquid. If a composite gem is cemented together, 
it may separate in boiling water, alcohol, or chloroform. 


Many gems can be altered in appearance, especially in 
color, by the application of radioactivity, heat, or chemi- 
cals. These agencies are, in fact, the ones that often nat- 
urally change the color of gems in the earth. Gems may 
be treated to meet the temporary whims of fashion, to 
improve the beauty of an inferior specimen, or to produce 
a distinctively different variety of a familiar gem. Al- 
though many kinds of gems are susceptible to treatment, 
only a few are systematically altered in the trade. 

When exposed to the emanations of radium, diamond 
not only becomes radioactive but turns green. Other 
gems are affected by this phenomenon, but they are of 
little commercial value. Any green diamond offered for 
sale should be suspected of having been thus doctored, 
even though natural green diamonds are not excessively 
rare. The artificially induced color seems to remain per- 
manently under normal conditions. 

The practice of heating yellow Brazilian topaz to a deli- 
cate pink yields a gem that has long been a favorite in 
fashionable jewelry, but the production seems to have 
declined lately because of economic reasons rather than a 
change in fashion. A much more active industry in Brazil 
is the creation of citrine, ranging in hue from light yellow 


to rich orange, by heating other varieties of quartz; crystals 
of amethyst give the best results, but uncut smoky quartz 
is more often used. 

Zircon is, of all the gems, by far the most important 
from the standpoint of heat treatment. The most popular 
hues blue, golden yellow, and colorless are derived from 
brown zircon. The exclusion of air from the charcoal 
furnace gives rise to the blue variety; the presence of air 
results in the golden variety. Colorless zircon is obtained 
both ways. 

Frequent attempts are made to improve the color of 
turquoise or restore the highly prized blue color after it 
has turned green. Few of them, however, are more than 
temporarily successful. 

The staining and dyeing of agate and other varieties of 
chalcedony quartz are so significant, involving an entire 
industry, that discussion of the methods used has been 
reserved for the chapter u Gems of the Silica Group." 


If not entirely man made, cultured pearls are at least 
man aided. Nature has been ably encouraged in her work 
of producing a lustrous gem from the misfortunes of a 
pearl oyster, which without interference might have lived 
comfortably and barrenly in the remoteness of the sea. 

The cause of pearl formation was discovered as early 
as the 13th century, when the Chinese took advantage of 
their knowledge and forced small metal images of Buddha 
between the shell and the mantle of fresh-water pearl 
mussels. The images became coated with nacre and were 
later removed as pearls. 


Somewhat over 50 years ago the Japanese, following a 
similar procedure, cemented a mother-of-pearl pellet to the 
inner lining of the shell and obtained a blister pearl, coated 
only on one side. 

Further experimentation culminated in the production 
by the Japanese of completely round pearls, the appear- 
ance of which in quantity in 1921 created a panic in the 
markets of the world until it was learned how they could 
be distinguished from the entirely natural gem. To these 
pearls the term cultured is applied, though some unsuccess- 
ful attempts have been made to confine it to the older 
artificially stimulated partial pearl (the blister pearl) and 
to refer to the whole pearl as cultivated. 

The equivalent of a surgical operation must be per- 
formed. A small bead made of mother-of-pearl is placed 
within a sac cut from the mantle of a three-year-old oyster, 
and the sac is then inserted in the tissues of another oyster, 
which covers it with nacre in the usual way during the 
succeeding seven years. At the end of that time the pearl 
appears as shown in Fig. 110. Both before and after they 
are treated, the mollusks are kept in cages suspended from 
rafts in the water and are repeatedly inspected by women 
divers (see Fig. Ill) for signs of disease. Owing to the 
usual hazards and uncertainties of living things, the per- 
centage of good-quality spherical pearls is small. 

Under pressure of a war economy, the Japanese pearl 
"farms," including the newly established one which pro- 
duced pink pearls in a fresh-water lake, were compelled 
to suspend operations. As the growing process cannot be 
unduly hastened, it will be perhaps 1952 before the indus- 
try can be fully re-established on an exporting basis. 


Fig. 110 Cultured Pearls after Seven Years' Growth 

Fig. Ill Woman Diver Tending Cultured Pearl Oysters 


When a mother-of-pearl bead serves as the nucleus of a 
cultured pearl, its presence makes possible several methods 
of distinguishing the product from a natural gem. A drilled 
pearl may be examined with an instrument called an en do- 
scope, which concentrates a beam of light into the hole. 
The light follows the concentric structure of a wholly 
natural pearl and is reflected out of the opposite end of 
the drill-hole; but it is deflected by the core of a cultured 
pearl and comes to the surface of the pearl at a different 
point. For undrilled pearls X-rays and special micro- 
scopes are employed to determine their origin. 


Chapter 8 

Luminescent Gems 

Few aspects of gemology have grown more in popular 
favor during recent years than the collection, display, and 
study of gems that glow in ultraviolet light. Because ultra- 
violet radiation is itself invisible, exposing such gems to it 
produces secondary colors that are not present in the 
original source of illumination. The gems glow or fluoresce 
in darkness that is complete, unless some extraneous reflec- 
tion of ordinary light has not been filtered out. When a 
gem continues to glow even after the ultraviolet rays have 
been turned off, it is said to phosphoresce. Both fluo- 
rescence and phosphorescence are combined under the 
general term luminescence. 

Neither of these effects is an exclusive response to ultra- 
violet radiation. Both may also be revealed by exposure 
to X-rays, cathode rays, or the emanations that result from 
radioactivity. These other methods sometimes produce a 
more intense luminescence than can be obtained from 
ultraviolet rays, but their use is greatly restricted because 
of expense, inconvenience, and danger. The development 
on a commercial scale of good sources of ultraviolet radi- 


ation has made it the most useful means of observing 
fluorescence and phosphorescence. 

Phosphorescence was studied before fluorescence. In 
1602 an Italian shoemaker noticed that specimens of barite, 
a heavy mineral which he had collected for his spare-time 
practice of alchemy, shone in the dark after they had been 
in a strong light. Proof was afterward found that this 
mineral, as well as other substances that behaved in the 
same way, could not be merely storing up sunlight or light 
from a fire and giving it off again, inasmuch as the color 
of the light underwent a change. 

The investigation of fluorescence led finally to the dis- 
covery of the underlying principles of both phenomena. 
A number of famous scientists, including Sir David 
Brewster, Sir John Herschel, and Sir George G. Stokes, 
worked on the problem. Stokes described the effect best 
and named it after the mineral fluorite, which often shows 
it. Much, of course, remains to be learned; even the real 
difference between fluorescence and phosphorescence is 
still open to discussion, as we shall presently see. 

Ultraviolet rays are of exactly the same nature as visible 
light and travel at the same speed. Both belong to the vast 
range of electromagnetic radiation, of which white light 
and its component colors represent only an extremely small 
part, about intermediate between the long, slowly vibrat- 
ing rays of wireless telegraphy and the very short, rapidly 
vibrating cosmic rays. As the wavelength of the radiation 
decreases and its frequency of vibration increases, the 
violet light of the visible spectrum gives way to the region 
that contains the invisible ultraviolet ("beyond the violet") 


In accordance with the observation that ultraviolet radi- 
ation on luminescent substances, including gems, gives rise 
to visible light, Stokes' law states that the resulting rays are 
always of longer wavelength than the primary rays. This 
law has since been disproved as a generalization, but it is 
usually correct. Another instance of the lengthening of 
rays is utilized in solar heating of homes; some of the visible 
sunlight that passes through the windows is changed into 
the longer infrared (heat) rays which are stopped by the 
glass and thus remain inside to heat the interior. Lumi- 
nescent gems act as transformers of light and change the 
wavelength of rays as an electrical transformer changes a 
given voltage. 

The analogy between the structure of atoms and the 
arrangement of our solar system the sun and its planets, 
including the earth is familiar. Electrons, which are par- 
ticles carrying a negative electrical charge, are assumed to 
revolve in definite orbits or shells around a central nucleus 
that has a positive charge, as the planets revolve in their 
concentric orbits around the sun. The impact of ultra- 
violet radiation upon luminescent substances causes them 
to absorb the added energy by displacing electrons to orbits 
farther out. This unstable condition is corrected when 
the electrons return to their original positions; the excess 
energy is given off in the form of luminescence. For 
luminescence to take place, therefore, absorption of energy 
must first occur. Previous absorption of energy distin- 
guishes phosphorescence of the kind referred to here from 
the familiar phosphorescence due to biochemical action, 
which results in the emission of light, often voluntarily, 
by fire-flies, glow-worms, certain fish, and other organisms. 

Besides these types of luminescence, there are a number 


of others, each with a special name. Luminescence may be 
produced by heat, friction, crystallization, cooling, and 
electrochemical action. Ultraviolet luminescence is the 
kind in which we are most interested. 

As impurities in gems, often in the most minute traces, 
have a great influence on the color, so also they have a 
profound effect on the nature and intensity of the lumi- 
nescence. Those impurities that cause luminescence are 
called activators, and those that prevent the effect are 
called inhibitors. This dependence upon small amounts of 
a foreign substance is a disadvantage in the identification 
of gems, because two stones of the same species but from 
different localities may fluoresce quite differently. It is an 
advantage, however, in classifying some gems according to 
origin, for some of the fluorescent colors in different lo- 
calities are distinctive. 

Impurities afford the basis for the present technical dif- 
ferentiation between fluorescence and phosphorescence. 
The latter term applies to crystalline substances only, 
whose power to give off light after they have been re- 
moved from the source of illumination is due to the pres- 
ence (as impurities) of atoms of metals which distort the 
crystal lattice. This condition differs from true fluo- 
rescence, which may occasionally persist for a very short 
time, but it is not possible to distinguish between the two 
types in this way under the circumstances with which the 
gemologist, mineral collector, or jeweler will ordinarily be 

The interest of American mineral collectors in the sub- 
ject of luminescence started with discoveries in connection 
with ivillewrite from Franklin, New Jersey. Only a rela- 


lively few specimens have ever qualified as gems, but they 
have been attractive ones, and the value of willemite as 
an ore of zinc has alone been great enough to make it sig- 
nificant among minerals. A fortuitous discovery was made 
by men working in the mine that the willemite could 
be distinguished from its associates (mostly franklinite, 
zincite, and calcite) by the bright green glow which it 
gave when exposed to the ultraviolet spark from an iron 
arc lamp. Research was undertaken to devise improved 
sources of ultraviolet radiation for the purpose of separat- 
ing willemite conveniently by this property; thus today's 
phenomenal fluorescent lighting industry began. Every 
ton of the New Jersey Zinc Company's ore that went 
into the recent world- wide fighting was concentrated under 
ultraviolet light. 

Some of the willemite continues to shine long after the 
ultraviolet rays are turned off. Such specimens are par- 
ticularly beautiful when they are mixed with patches of 
white calcite which fluoresce a fine red color. 

Not all willemite, however, fluoresces or phosphoresces. 
When it is pure, as in a few localities elsewhere in the 
world, this zinc silicate shows no evidence of either effect. 
Traces of manganese present in the New Jersey material 
give it the highly prized luminescence. 

Fluorescent diamonds now appear to be much more 
abundant than they were formerly thought to be. Per- 
haps sixty-five per cent show this wonderful effect. The 
King of Gems may glow with varying intensity in almost 
any color. Sky blue or cornflower blue is the most typical 
of the stones from South Africa, though green and yellow 
are not uncommon. An occasional diamond phospho- 
resces and will be seen to glow in the dark after it has 


been exposed to sunlight; the most phosphorescent stones 
are those which fluoresce in daylight. Three hundred years 
ago the British scientist Robert Boyle experimented with 
diamonds that emitted light after being rubbed against 
fabric or wood; this type of luminescence is called tribolu- 
tmnescence. Boyle also noted that diamond fluoresces 
when heated; the property is called thermolwninescence. 

Ruby, above all others, seems to deserve the distinction 
of being the chief luminescent gem. It does not react more 
strongly than some other stones, but it owes a large part 
of its glorious beauty to its rich scarlet fluorescence, which 
appears even in ordinary sunlight and serves to heighten 
the natural color of the gem and to make it superior to 
any other red stone. Rubies from Burma and Ceylon 
show more fluorescence than those from Siam. 

If they are colored by chromium, red spinel and (to a 
lesser degree) pink spinel show a similar addition of fluo- 
rescence to their normal color. A similar effect of bright- 
ening can also be observed. 

It is most appropriate to mention the fluorescence of 
fiuorite, since that gem mineral gave its name to the phe- 
nomenon. Unfortunately for the nomenclature, a large 
proportion of fluorite is not visibly affected by ultraviolet 
radiation. The specimens that do respond usually show a 
blue-violet color, which is ascribed to the presence of rare- 
earth elements. 

Kunzite, the lilac variety of spodumene, phosphoresces 
strongly in a fine pink hue. 

Opal varies in its fluorescence, some specimens glowing 
only after they have been subjected to ultraviolet light for 
several minutes. Bluish and yellowish colors are common. 
The bright green of some opal is attributed to the presence 


of radioactive substances, secondary uranium compounds. 
The yellowish-green fluorescence of common opal from 
Virgin Valley, Nevada, is very familiar to American col- 

Examination of museum specimens of jade has showed 
that ageing may often be detected by the change in color 
of fluorescence, which declines from an intense purple in 
newly cut jade to white with blue and yellow mottling. 

Amber fluoresces strongly, the color ranging from 
yellowish green to bluish white; the latter is most frequent. 

Pearls fluoresce according to the waters from which the 
oysters were taken. The majority of those used in jewelry, 
from Ceylon, the Persian Gulf, and Australia, show a sky- 
blue color. The ethereal blue of Japanese cultured pearls 
is most appealing. An interesting difference between the 
fluorescence of cultured pearls and natural pearls is seen 
during their exposure to X-rays. Although the produc- 
tion of these rays for gem testing is generally not feasible, 
the standard apparatus for differentiating pearls, called an 
endoscope, uses X-rays. With them, cultured pearls are 
found to be by far the more fluorescent of the two types, 
especially when they have a mother-of-pearl bead as a 

To return to the corundum gems, other varieties be- 
sides ruby may be mentioned in connection with fluo- 
rescence. Yellow corundwn fluoresces strongly in golden 
yellow. Blue corundum varies in intensity; stones from 
Montana and Ceylon glow more strongly than those from 

Synthetic ruby fluoresces vividly, even more than the 
natural gem, owing to its greater content of chromium. 


Certain colors of synthetic spinel display fluorescence in 
its choicest form. The yellowish-green stones, fluorescing 
in the same color, are particularly striking. The blue 
stones fluoresce brightly in red. The red fluorescence of 

Fig. 112 Fluorescent Effects in Several Varieties of Quartz 
and Chalcedony 

the recently developed American synthetic emerald serves 
as the easiest, though not the surest, means of distinguish- 
ing it from natural emerald, which usually does not flu- 
oresce in ultraviolet light. 

Other gems besides those discussed here (see Fig. 112) 
display occasional luminescent colors, which are so variable, 
depending so much upon the locality, that descriptions of 
them would resolve into a mere listing. The best way to 


become familiar with them is to see them in museums and 
to build a collection of them with which to experiment 
at home. 


The most important fact to be considered when equip- 
ment is being acquired for the production of fluorescent 
light is that, although the ultraviolet wavelengths cover 
only a tiny fraction of the electromagnetic series, they 
nevertheless extend over a wider range than is covered by 
any single source of illumination. More than one lamp 
is needed if all the fluorescent effects are to be obtained. 
A lamp designed for one part of the field will fail to 
illuminate the stones that respond only to a different part, 
for gems and minerals vary in their reaction to different 
radiation. In general, the available equipment is made 
for either "long" or "short" wavelengths, the latter being 
more desirable for most purposes. The ultraviolet range 
is about 1600 to 3800 angstrom units (A.U.), whereas the 
visible spectrum extends from 3800 to 8000 A.U., each of 
these units being one hundred-millionths of a centimeter 
in length. 

A second essential fact to be remembered about fluo- 
rescent apparatus is that each of the lamps transmits a 
certain amount of visible light, which dilutes the fluo- 
rescence and confuses the effect. Consequently, a filter 
must usually be employed to eliminate as much of the day- 
light colors as possible. The proper filter depends, of 
course, upon the range of the lamp with which it is to be 
used. Care should be taken to protect one's eyes from the 
harmful effects of the invisible rays. 


Besides a wide range of ultraviolet radiation, an ideal 
fluorescent lamp gives an intense and uniform illumination, 
free from unpleasant fumes or excessive heat, and capable 
of being enclosed for protection. An ideal filter transmits 
all the i^ltraviolet and none of the visible light. Some of 
the equipment made today approaches perfection in many 

Any discussion of ultraviolet sources should begin with 
the sun, for sunlight is rich in these rays. Much of the 
beauty of ruby is the result of its fluorescence in sunlight 
added to its natural color. Much fluorite, many dia- 
monds, and some amber, opal, and kunzite are made 
lovelier in this manner. 

Stokes used lightning in some of his studies of fluo- 
rescence, but this extreme method is scarcely recom- 
mended to the general public. 

The cheapest and most convenient source of ultraviolet 
light is the argon bulb, shown in Fig. 113. It is similar 
in principle to the familiar neon sign except that it is 
filled with argon (mixed with other gases) and can be 
used like any electric light bulb on ordinary house current. 
Although quite weak, it is surprisingly effective with some 
gems. The glass prevents the transmission of short wave- 
lengths, passing those from 3300 to 3700 A.U., the peak 
being at about 3600 A.U., but practically none of the 
energy is wasted in delivering heat; so little visible light 
is produced that no filter is needed. 

Another source of ultraviolet light that does not require 
a filter is the high-potential spark between iron electrodes. 
The apparatus consists of a transformer, a condenser, and 
a pair of adjustable electrodes. Unlike the argon bulb, 


this radiation is rich in the shorter wavelengths. It has a 
low intensity but is convenient for its range. 

The true iron arc is a high-intensity, low-voltage arc 
between iron electrodes. It operates best on direct cur- 
rent and gives off a large amount of visible light which 
must be filtered out. 

Fig. 113 Argon Bulb and Reflector for Producing Ultraviolet 


[Ultra- Violet Products.] 

The carbon arc gives large amounts of heat and visible 
light, but it combines the advantages of high intensity and 
wide range of wavelengths. 

Of the various types of equipment the most suitable for 
the ultraviolet examination of most gems and minerals is 
some form of mercury vapor lamp, two kinds of which 
are shown in Figs. 1 14 and 115. The visible violet color of 
the incandescent gas is used in modern sign and street 
lighting. When a fused silica ("quartz") tube is used as 
the container, both high intensity and wide range, with 
the shorter wavelengths predominating, are obtained. An 


Fig. 114 Lamp and Filter for Museum and Commercial Use 

Fig. 115 Portable Model for Display or Field Use 

Mercury Vapor Lamps for Creating Luminescence 

[Ultra- Violet Products.] 

excellent ultraviolet source when it is equipped with an 
appropriate filter is the genmcidal lamp now widely used. 
A nickel-cobalt glass tube is convenient for museum in- 
stallations, but it reduces the fluorescence as well as the 
amount of visible light. The same kind of glass is used in 
a bulb shape for the so-called hot bulb, which combines 
mercury vapor with a heating filament. 

All this equipment, together with the newest improve- 
ments, is advertised regularly in popular mineral maga- 
zines. Manufacturers' catalogues supply detailed infor- 
mation about each article. 



A/lore extensive information regarding gems will be 
found in the following books and periodicals, which have 
been selected as the most suitable to supplement Popular 
Gewology. Some of the books are of a general nature 
and others emphasize special phases of gemology. All are 
standard works, modern in content and authoritatively 
written. The brief descriptive notes are intended to aid 
the prospective purchaser. 


Ge-mstones, by George F. Herbert Smith. 9th edition, 
1940. Published by Methuen, London. Price 18 shillings. 
This edition is the most complete modern book on gems 
in English. Parts of it are highly technical; the book is 
scholarly and interesting throughout, and especially good 
for reference. It contains 443 pages, with many illustra- 
tions and colored plates, and an extensive bibliography. 

Gews and Gem Materials, by Edward H. Kraus and 
Chester B. Slawson. 5th edition, 1947. Published by 
McGraw-Hill, New York. Price $4.00. This excellent 
technical book on gems is written in concise textbook 
form. The style is consequently brief and clear, and there 
is little detail in the descriptions of individual gems. It 


contains 332 pages, many illustrations, and a valuable sum- 
marizing table. 

Gem Testing 

Gem Testing, by B. W. Anderson. 2nd edition, 1947. 
Published by Hey wood, London. Price 17 shillings 6 
pence. This is the first book of its kind; it was formerly 
titled Gem Testing for Jewellers but is suitable for every- 
one. There are 23 chapters written simply and in detail, 
with the admirable purpose of explaining things to the 
reader as clearly and as practically as possible. It con- 
tains 194 pages, illustrations, and a glossary. 

Handbook of Gem Identification, by Richard C. Liddi- 
coat, Jr., 1947. Published by Gemological Institute of 
America, Los Angeles. Price $4.50. Methods of testing 
gems and descriptions of instruments used are well pre- 
sented. It contains 283 pages, illustrations, tables, and a 

Gem Cutting 

The Art of Gem Cutting, by H. C. Dake and Richard 
M. Pearl. 3rd edition, 1945. Published by the Mineralo- 
gist Publishing Company, Portland, Oregon. Price $1.50. 
This book meets the popular demand for a complete text 
on the lapidary aspects of gemology. It gives detailed 
instructions on the materials and equipment used. It con- 
tains 128 pages and is well illustrated with drawings and 

Gem Glossary 

Dictionary of Gems and Gemology, by Robert M. 
Shipley and others. 2nd edition, 1946. Published by 


Gemological Institute of America, Los Angeles. Price 
$5.50. This glossary defines over 4,000 names of gems 
and terms used in gemology. Incorrect nomenclature 
is adequately indicated, and cross references are numerous. 
It contains 258 pages. 

Quartz Gems 

Quartz Family Minerals, by Henry C. Dake, Frank L. 
Fleener, and Ben Hur Wilson, 1938. Published by Whit- 
tlesey House, New York. Price $2.50. This book is writ- 
ten especially for gem and mineral collectors, for whom 
the quart/, varieties have the widest appeal. Every aspect 
is discussed; producing localities are emphasized, and there 
are separate chapters on opal and petrified wood. It con- 
tains 304 pages and is well illustrated. 


The Mineralogist Magazine is published monthly at 329 
S.E. 32nd Street, Portland 15, Oregon. Its widely read 
gem department features illustrated articles on gems, new 
methods and equipment pertaining to gem cutting, and 
gem localities. Editor, Dr. H. C. Dake. Subscription 
price is $2.00 per year. 

Rocks and Minerals is published monthly at Peekskill, 
New York. It includes articles on gems and gem min- 
erals, with emphasis on collecting localities in the eastern 
part of the United States. Editor, Peter Zodac. Subscrip- 
tion price is $3.00 per year. 

Geim and Gemology is published quarterly by the 
Gemological Institute of America, 541 South Alexandria 


Avenue, Los Angeles 5, California. It is issued especially 
for members of the institute but is available to other in- 
terested persons. Editor, Robert M. Shipley. Subscrip- 
tion price is $3.50 per year. 

The Gevrwologist is published monthly by the National 
Association of Goldsmiths Press, 226 Latymer Court, Lon- 
don. It is an established journal devoted exclusively to 
gems. Editor, Arthur Tremayne. Subscription price is 
12 shillings per year. 

The Desert Magazine is published monthly at El Centro, 
California. It features colorful articles on gem localities 
in southwestern United States, with cleverly illustrated 
maps to guide the collector. Editor, Randall Henderson. 
Subscription price is $3.00 per year. 

The Lapidary Journal is published bimonthly at 1129 
North Poinsettia Place, Los Angeles 46, California. It 
specializes in gem cutting for the amateur. Editor, Le- 
lande Quick. Subscription price is $2.00 per year. 



Abalone, pearl in, 237 
Abrasion, 55 

Absorption of light, 26, 30 
Absorption band, 42 
Absorption spectrum, 12, 42, 145 
Achroite, 128 

Acid, effect of, on gems, 13, 14 
Acid igneous rock, 66 
Actinolite, 191 
in prase, 214 
in sagenite, 209 
Activator, 273 
Adamantine luster, 31 
Adular Mountains, moonstone 

from, 178 
Adularia, 178 

Afghanistan, gems from, 101, 107, 183 

Africa, gems from, 68, 87, 88, 91, 

126, 157, 231, 240; see also 

names of countries 

East, gems from, see East Africa 

South, gems from, see South 

South, Union of, see Union of 

South Africa 

South-West, gems from, see 
South-West Africa 

Agalmatolite, 201 

feel of, 63 
Agate, 213, 217, 221 

banded, 219 

dyed, 266 

eye, 218 

flower, 217 

fortification, 218, 220 

iris, 218 

landscape, 217 

marking in, 23 

moistening, 31 

moss, 216 

miniatures in, 72 

occurrence of, 65 

plume, 217 

scenic, 217 

seaweed, 217 

tree, 217 
Agate opal, 229 
Agatized wood, 222 
Alabaster, 198 

Alaska, gems from, 145, 192 
Albite, 177, 178, 179, 180 

moonstone, 178, 180 
Alexander the Great, 132 
Alexander II, 108 


Alexandrite, 108 

absorption spectrum in, 44 

crystallization of, 21 

synthetic, 252 

synthetic spinel resembling, 256 
Alkali, caustic, effect of, on em- 
erald, 13 

Alkali feldspar, 178, 180 
Allochromatic gem, 28 
Alluvial deposits, see Placers 
Alluvial diamond, 68, 87 
Almandine, 145 
Almandine spinel, 106 
Almanditc, 143, 144 

absorption spectrum in, 44 

in composite gems, 264 
Almandite series, 143 
Alps, gems from, 158, 195, 207, 


Altered gems, 151 
Aluminates, 12 
Aluminum, abundance of, in gems, 


Amateur lapidary, 202, 213 
Amatrix, 172 
Amazonite, 178 
Amazonstone, 178 

crystallization of, 22, 176 
Amber, 8, 233, 240 

composition of, 12 

effect of ether on, 14 

electricity in, 62 

fluorescence of, 276, 279 

from Baltic Sea, 68 

heat test for, 64 

imitation, 261 

insects in, 243 

luster of, 31 

origin of, 69 

salt water test for, 53 

specific gravity of, 55 

Amber, used for goiter, 3 

Amber oil, 242 

Amber pitch, 242 

Amber varnish, 242 

Ambergris, 244 

Ambroid, 244 

American cut, 73 

American Gem Society, 4 

American Museum of Natural 

History, 115, 136 
Amethyst, 204 

cause of color in, 28 

crystallization of, 21 

resemblance to cordierite, 117 

treated, 266 
Amethyst sapphire, 98 
Amorphous gems, 16, 231, 246 

absence of cleavage in, 60 

absence of tlichroism in, 45 

effect of light on, 39, 40, 41 

fracture in, 60 

polarization in, 48 
Amphibole group, 190 
Amsterdam, diamond cutting in, 


Amulets, gems used as, 1, 2 
Andalusite, 158, 196 

crystallization of, 21 

polymorphism of, 15 
Anderson, B. W., 284 
Andes Mountains, Chile, lapis la- 
zuli in, 183 
Andesinc, 179 
Andradite, 143, 147 

dispersion in, 38 

luster of, 31 
Andradite series, 143 
Angola, diamond in, 88 
Animal gems, 233 
Animal products, distinguished 
from minerals, 6 


Anodonta, 237 
Anorthite, 179 
Antero, Mount, Colorado, gems 

from, 135, 136, 140 
Ant hills, olivine in, 139 
Antigorite, 200 

Antwerp, diamond cutting in, 94 
Apatite, 1 1 5 

crystallization of, 21 

hardness of, 56 
Apollo Belvedere, 205 
Apostles, gems of the, 5 
Aquamarine, 131, 134; see also 

chrysolite, 134 

crystallization of, 20 

resemblance to euclasc, 154 

synthetic, 253 

synthetic spinel resembling, 256 

X-ray picture of, 24 
Aqua regia, effect of, on gems, 


Arabia, pearl from, 237 
Aragonite, in pearl, 234, 235 
Arc, carbon, 280 

iron, 280 

Argon bulb, 279, 280 
Arizona, Canyon Diablo, 98 

gems from, 139, 144, 170, 173, 

194, 223, 231 
Arizona ruby, 102, 144 
Arkansas, gems from, 90, 208 
Arrows of love, 209 
Artificial gems, 8, 247 
Art of Gem Cutting, The, 284 
Aru Islands, pearl from, 238 
Asbestos, 191, 200, 210 
Asia, see names of countries, Asia 
Minor, Banka, Middle East 

Asia Minor, gems from, 172, 199, 
228, 245; see also names of 

Asparagus-stone, 1 1 5 

Assyria, lapis lazuli used in, 182 

Asterism, 50, 102, 103, 250 

Atlantic Ocean, coral from, 240 

Atomic structure, see Structure, 

Atoms, 7, 16, 23, 24, 26, 55, 141 

Australia, gems from, 57, 89, 104, 
112, 139, 146, 157, 159, 170, 
174, 193, 226, 227, 232, 237, 
240, 276; see also New 
South Wales, Queensland, 
South Australia, Tasmania 

Austria, gems from, 119, 134, 154, 
162, 195 

Aventurinc, 206 

Avcnturine feldspar, 180 

Axinite, 158 
crystallization of, 22 

Axis, crystal, 17 

Aztec jade carving, 187 

Aztecs, obsidian used by, 230, 231 

Azurite, 169, 170, 193 

Azurmalachite, 171 

Babylonia, lapis lazuli used in, 182 
Baguette cut, 73 
Bakelite, 261 

salt water test for, 53 
Balas ruby, 106 
Ball, Sydney H., 65 
Ballas, 97 

Baltic Sea, amber from, 68, 240 
Banded agate, 219 
Band, absorption, 42 
Banka, cassiterite from, 112 
Bantam, 65 
Barite, fluorescence of, 271 


Baroque pearl, 235 
Basic igneous rock, 66 
Bavaria, spessartite from, 146 
Bay of Fundy, pearl essence from, 

Beauty of gems, 8, 24, 25, 26, 55 

effect of refraction on, 32 
Bcccka diamond mines, 88 
Belgian Congo, gems from, 88, 91, 


Belgium, diamond cutting in, 94, 95 
Bending of light, 32 
Benitoite, 114, 122 

crystallization of, 21, 123 

dichroism in, 46 

double refraction in, 40 
Berman, Harry, 74, 164 
Beryl, 131; see also Aquamarine, 

composition of, 12 

crystallization of, 20, 21 

emerald, absorption spectrum in, 

synthetic, 134, 248, 256, 260, 264 

X-ray picture of, 24 
Beryl glass, 260 
Biaxial gem, 40 

dichroism in, 44 

optic axes in, 41 
Bible, birthstones in, 4, 5 

gems mentioned in, 138, 182, 214 
Billiton, cassiterite from, 112 
Birefringence, 39, 41 

table, 42 

Birthstones, 4, 5, 100, 102, 131, 155 
Bivalve mollusk, 237 
Blacas Medusa head, 205 
Black coral, 240 

Black Hills, South Dakota, petri- 
fied wood from, 223 
Black opal, 224, 226 

Black Prince, 105 
Black Prince's ruby, 105 
Blackjack, 111 
Blende, 111 
Blister pearl, 235, 267 
Bloodstone, 215 
Blowpipe tests, 64 
Blue earth, 240 
Blue ground, 77 

loading, 79 
Blue-John, 112 
Blue spinel, 256 
Blue white diamond, 94 
Bohemia, gems from, 144, 231; see 

also Czechoslovakia 
Bohemian garnet, 143 
Bolivar, Simon, 94 
Bolivia, cassiterite from, 112 
Bonded diamond wheel, 95 
Bone, 262 

Bone turquoise, 174 
Books, selected, 283 
Borneo, gems from, 57, 89, 96, 

232, 238 
Bort, 96 

Dutch, 153 
Bottle stone, 232 
Boule, 250, 252, 253, 255 
Bowenite, 200 
Boyle, Robert, 275 
Bracelet, 2 

Braganza diamond, 156 
Brazil, gems from, 87, 89, 97, 109, 
110, 115, 116, 119, 120, 121, 
122, 126, 127, 129, 134, 135, 
136, 137, 139, 140, 145, 146, 
155, 156, 157, 159, 161, 196, 
197, 206, 207, 208, 213, 219 

heating gems in, 265 

itacolumite in, 223 

pinking topaz in, 155 


Brazilian emerald, 124, 128 

Brazilian peridot, 128 

Brazilian sapphire, 128 

Brazilianite, 114 
crystallization of, 22 

Breakage, resistance to, 61 

Breastplate of judgment, 5 

Brcwster, Sir David, 271 

Bridgman, Percy W., 259 

Brilliancy, 38 
of diamond, 33 

Brilliant cut, 71, 133 

Brilliants, 261 

British Columbia, Canada, sodalite 
in, 181 

British Guiana, diamond in, 89 

British Imperial State Crown, 105 

British Museum of Natural His- 
tory, 156 

Bromoform, 53 

Bronzite, 118 

Bulb, argon, 279, 280 
hot, 282 

Bultfontein diamond mine, 88 

Burma, gems from, 100, 104, 106, 
110, 116, 118, 119, 126, 137, 
146, 157, 160, 161, 177, 183, 
190, 243, 275 

Burma Ruby Mines, Ltd., 101 

Burmese amber, 243 

Burmitc, 243 

Button pearl, 236 

Bytownite, 179 

Cabochon gems, 70, 71, 163, 203 
Cachalong, 229 
Cairngorm, 212 
Calamine, 167 
Calcite, 45, 274 

double refraction in, 39 

hardness of, 56 

Calcite, in amber, 243 

in coral, 239 

in lapis lazuli, 183 

in pearl, 234, 235 

polarization in, 48 
Calcium, abundance of, in gems, 


California, gems from, 122, 123, 
125, 127, 136, 157, 173, 180, 
183, 192, 195, 197, 214, 217, 

Calif ornite, 194 
Cameo, 2, 71 

Canada, gems from, 162, 180, 181, 
223; see also British Colum- 
bia, Labrador, Newfound- 
land, Ontario, Quebec 

pearl essence from, 262 
Cane, glass, 261 
Canyon Diablo, Arizona, 98 
Cape ruby, 102, 144 
Carat, 51, 52 
Carbon arc, 280 
Carbonado, 96 
Carbonates, 12 
Carbuncle, 145 
Card test, for double refraction, 


Caribbean Sea, pearl from, 238 
Carnelian, 213, 222 
Carved gems, 72, 186, 187 
Carving, gem, 163 
Cassiterite, 112 

crystallization of, 19, 20 

dispersion in, 38 

double refraction in, 40 

specific gravity of, 55 
Catalin, 261 

Catherine the Great, 205 
Cathode rays, in luminescence, 270 


Cat's-eye, chatoyancy in, 50 
chrysoberyl, 108 
crystallization of, 21 
diopside, 119 
quartz, 210 
scapolite, 116 
sillimanite, 160 
tourmaline, 128 
Catskill Mountains, New York, 

petrified wood from, 223 
Caustic alkali, effect of, on em- 
erald, 13 
Celluloid, 261 
Centennial Exposition, aniazon- 

stone at, 179 

Central America, gems from, 119, 
189, 238; see also na?nes of 
jade used in, 186 
Ceramic material, 262 
Certified Gemologist, 4 
Ceylon, gem mining in, 152 
gems from, 99, 101, 104, 106, 
108, 109, 110, 117, 119, 124, 
126, 136, 137, 139, 145, 146, 
152, 159, 160, 177, 206, 210, 
237, 275, 276 
gravel deposits in, 68 
Ceylonese peridot, 128 
Ceylonite, 106 
Chalcedony, 203, 212 
color in, importance of, 26 
dyed, 266 

fluorescence of, 277 
formed by springs, 69 
imitative shapes of, 23 
in geode, 68 

in opal doublet, 228, 264 
in petrified wood, 14 
Characteristics of gems, 8 
Charlemagne, 132 

Charlotte, Queen, 205 
Charms, gems used as, 1 
Chatoyancy, 50 

in chrysoberyl cat's-eye, 109 

in hawk's-eye, 211 

in quartz cat's-eye, 210 

in tiger's-eye, 210 
Chemical action on gems, 55 
Chemical composition, of gems, 11 

of minerals, 7 
Chemical precipitates, 67 
Chemical properties of gems, 25 
Chemical resistance of gems, 12 
Chemical tests, 11, 13, 14, 25 
Chemicals, effect of, on color, 28 

treating gems with, 265 
Chemistry, of gems, 11 
Chiastolite, 159, 196 
Chicago Natural History Museum, 


Chile, lapis la/Aili from, 183 
China, amber imported into, 243 

carved jade from, 186 

gems from, 184, 200, 238 

hematite cut in, 166 

jade used in, 185 

lapis lazuli used in, 182 

pearl culture in, 266 

Wyoming nephrite carved in, 


Chinese cat's-eye, 110 
Chivor, Colombia, emerald from, 


Chlorastrolite, 184 
Chloromelanite, 189 
Chlorospinel, 106 
Chrysoberyl, 107 

chrysolite, 110 

composition of, 12 

crystallization of, 21 

twin crystal of, 17 


Clirysoberyl cat's-eye, 210 

chatoyancy in, 50 
Chrysocolla, 193 
Chrysolite, 139 

confusion of name with topaz, 


Chrysolite aquamarine, 134 
Chrysolite chrysoberyl, 110 
Chrysoprase, 214 

imitated in agate, 221 
Chrysotile, 200 
Cinnamon-stone, 146 
Citrine, 206, 212 

resemblance to topaz, 155 
Clam, pearl in, 2*7 
Class, crystal, 17 
Cleaning diamond, 87 
Cleaning jewelry, 87 
Cleavage, 55, 59 

in diamond, 86 
Cleavage face, luster of, 31 
Cleaver, diamond, 86 
Cleaving, diamond, 63 
Cleopatra, 13, 132 
Clerici's solution, 53 
Climate, 69 
Cohesion, 55, 59 
Colombia, emerald from, 133 
Colophony, 242 
Color, 25, 42 

analyzing, instruments for, 29 

cause of, in gems, 11 

change of, caused by heat, 64 

of diamond, 94 

use of, in identification of gems, 


Colorado, gems from, 113, 135, 
136, 140, 144, 146, 153, 158, 
173, 176, 179, 184, 199, 212 
Colorado ruby, 144 

Colorless gems, absence of dichro- 

ism in, 46 

Common coral, 239 
Common opal, 225, 229 
Composite gems, 134, 143, 247, 263 
Concentrating methods, diamond, 


Conch, pearl in, 237 
Conchiolin, 234, 235, 236 
Conchoidal fracture, 61 
Conglomerate, jasper in, 215 
Connecticut, gems from, 122, 126, 

136, 137, 154, 184 
Concjuistadores, 133 
Coober Peby opal field, 226 
Copal, 244 

Copper cent, hardness of, 59 
Coral, 8, 233, 238 

color in, importance of, 26 

composition of, 12 

effect of acid on, 13 

effect of oil of turpentine on, 13 

occurrence of, 69 
Cordierite, 117 

crystallization of, 21 
Core drill, diamond, 96 
Cornelian, 213 
Cornwall, England, cassiterite 

from, 112 

Corporation, Diamond, 90 
Corundum, 98; see also Ruby, 

asterism in, 50 

composition of, 12 

crystallization of, 20 

fluorescence of, 275, 276 

hardness of, 56 

isomorphism in, 14 

parting of, 60 

ruby, absorption spectrum in, 43 
dichroism in, 46 


Corundum, sapphire, dichroism in, 

synthetic, 108, 248, 249, 264 
Coscuez, Colombia, emerald from, 


Cosmic gems, 65, 69, 98, H9, 232 
Cristobalite, 202 
Critical angle, 33, 34, 35 
Crocidolite, 210, 211 
Cross stone, 196 
Crossed polarizers, 49 
Crossed tourmaline, 48 
Crown glass, 260 
Crusaders, 133, 138 
Cryptocrystalline quartz, 20 > 
Cryptocrystalline structure, in 

chalcedony, 212 
Crystal, 15, 20?' 

phantom, 15 
Crystal axis, 17 
Crystal class, 17 
Crystal form, 16, 17, 18, 19, 59 

related to atomic structure, 7 

use of, in identification of gems, 


Crystal gazing, 207 
Crystal structure, 15, 16, 17, 18 
Crystal system, 17, 18 
Crystalline gems, 16 

cleavage in, 59, 60 

fracture in, 60 

hardness of, 57 
Crystalline quartz, 203, 212 
Crystallization, related to optical 

properties, 18 
Crystallography, 15 
Crystals, testing, for hardness, 58 

twin, 16, 17 

Cuba, diamond cutting in, 95 
Cube, 91, 165 
Cullinan diamond, 92, 93 

Cultivated pearl, 267 
Cultured gem, 247 
Cultured pearl, 238, 266 

fluorescence of, 276 
Cumberland, England, hematite in, 


Cupid's darts, 209 
Cushion cut, 73 
Cutter, diamond, 86 
Cutting, diamond, with electric 

arc, 97 
of gems, 70, 71, 73, 74 

effect of dichroism on, 49 
of synthetic ruby, 253 
Cutting centers, diamond, 94 
Cyanitc, 160 

Cycad Forest National Monu- 
ment, South Dakota, 223 
Cylinder, 2 
Cymophane, 109 
Czechoslovakia, gems from, 197, 

226, 231; see also Bohemia 
manufacture of imitations in, 

Dakc, Henry C., 74, 284, 285 
Dana's Systeju of Mineralogy, 74, 

Danburite, 137 

crystallization of, 21 

resemblance to datolite, 154 
Datolite, 154 

crystallization of, 22 

with prehnite, 184 
Datolite family, 154 
De Beers Consolidated Mines, Ltd., 


De Klerk, 65 
Demantoid, 147 

absence of dichroism in, 46 


Dcndritcs, in chalcedony, 216 

in moss opal, 229 

on marble, 23 
Dendritic marble, 23, 198 
Density, 52, 53 

optical, 32 
Derbyshire, England, fluorite at, 


dc Saussurc, Horace B., 195 
Desert Magazine, The, 286 
Devil's Head, Colorado, topaz 

from, 158 
Diamond, 75 

alluvial deposits, 68, 87 

atomic structure of, 7, 57 

brilliancy of, 33 

cleavage of, 86 

color of, 94 

composition of, 12 

critical angle in, 33, 34 

crystal form of, 19, 91 

cutting, 71, 73, 86 
centers, 94 

cleavage used for, 60 
orientation in, 91 
with electric arc, 97 

discovery of, 65, 76 

dispersion in, 37 

effect of radioactivity on, 265 

electricity in, 62 

emerald cut, 73 

famous stones, 93 

fluorescence of, 279 

gems found with, 65 

hardness of, 56, 57, 58 

Herkimcr, 209 

in meteorites, 69 

industrial, 95 

luminescence of, 274 

luster of, 31 

mining of, 77, 79 

Diamond, name of, origin of, 91 

occurrence of, 87, 88, 89, 90, 

origin of, 97 

polishing of, 31, 87 

polymorphism of, 15 

recovery of, 80 

refractive index of, 33, 38 

resemblance to sphcnc, 162 

resemblance to zircon, 153 

specific gravity of, 52, 53 

synthetic, 258 

twinning in, 57 
Diamond core drill, 96 
Diamond Corporation, 90, 95, 96 
Diamond Corporation of America, 


Diamond die, 96 
Diamond doublet, 263, 264 
Diamond mines, other gems from, 

118, 119, 139, 144, 153 
Diamond pipe, geology of, 77 

occurrence of, 67 
Diamond point, 71 
Diamond powder, grading of, 97 
Diamond Trading Company, 91 
Diamond wheel, bonded, 95 
Diatomaceous earth, 229 
Dichroism, 44, 49 
Dichroite, 117 

Dichroscope, 29, 45, 46, 48, 49 
Dictionary of Gems and Gem- 

ology, 284 
Die, diamond, 96 

Diffraction of light, in pearl, 236 
Diffusion column, 53 
Dinosaurs, 75 
Diopside, 118, 119, 190 

crystallization of, 22 

occurrence of, 65 


Diopside, with idocrase, 195 
Direct-vision spectroscope, 42, 43 
Dirigeni, 248 
Dispersion, 37 

table, 38 
Disthcne, 160 
Dodecahedron, 91 
Dop, 86, 87 

Double refraction, 39, 44, 45, 46, 
48, 49 

card test for, 40 
Doublet, 263 

opal, 228 
Doubly refractive gems, 35, 36 

polarization in, 48 
Dravite, 128, 130 
Dresden diamond, 93 
Drill, core, diamond, 96 
Drying, of opal, 64 
Dumortier, Eugene, 197 
Duniorticritc, 197 
Durability, 55 

of gems, 8 
related to chemical resistance, 


Dust pearl, 236 
Dutch bort, 153 

Dutoitspan diamond mine, 79, 88 
Dyed agate, 220, 266 
Dyed chalcedony, 266 


Eacret, Godfrey, 122 
East Africa, gems from, 112, 140, 

155, 161 

East Prussia, amber from, 241 
Ebelman, 250 
Eden Valley, Wyoming, petrified 

wood from, 223 

Effervescence, of carbonate gems 
in acid, 14 

Egypt, amethyst used in, 205 

gems from, 132, 138, 172 

manufacture of gems in, 246 

turquoise used in, 172 
Egyptian jasper, 215 
Elba, gems from, 126, 127, 166 
Electric arc, for diamond cutting, 

Electricity, 62 

in amber, 241 
Electron, 272 

Electronics, use of quartz in, 63 
Elektron, 241 

El Libertador diamond, 94 
Emerada, 248 
Emerald, 131, 132; sec also Beryl 

absorption spectrum in, 44 

Brazilian, 128 

brittlcncss of, 61 

cause of color in, 11, 28 

crystallization of, 20 

dichroism in, 46 

effect of caustic alkali on, 13 

evening, 138 

fracture of, 60 

imitation, flaws in, 132 

soude, 264 

synthetic, 134, 248, 256, 260, 264 
fluorescence of, 277 

use of, in Rome, 224 

X-ray picture of, 24 
Emerald cut, 73, 133 
Emerald triplet, 263 
Emerald veins, occurrence of, 67 
Emperor Kao-tsung, 188 
En cabochon, 163 
Enamel, 262 
Endoscope, 269 
England, gems from, 112, 113, 166, 

240, 245 
Engraving, gem, 2, 3, 163 


Enstatitc, 118, 190 

with diamond, 118 
Enstatite scries, 118 
Epaulet cut, 73 
Epidotc, 147 

crystallization of, 22 
Epidote group, 195 
Equipment, fluorescent, 278 
Erinidc, 248 
Erosion, 67 
Essence, pearl, 262 
Este, Star of, diamond, 93 
Ether, effect of, on amber, 15 
Ethics of the Dwi, 127 
Etruscans, amethyst used by, 205 
Etta Mine, South Dakota, spodu- 

mene from, 120 
Euclasc, 154 

crystallization of, 22 
Europe, see ucrmes of countries 

jet used in, 245 

Europe, central, gems from, 112, 
154, 189; see also names 
of countries, Mediterranean 
Sea, Mediterranean islands 
Even fracture, 61 
Evening emerald, 138 
Extinction, 48 
Eye agate, 218 

Faceted gems, 70, 203 
Faceting diamond, 84 
Faceting device, 75 
Fairy stone, 159, 196 
False cleavage, 60 
Families, gem, 9, 10 
Famous diamonds, 92 
Farm, cultured pearl, 267 
Farming, of diamond, 80 
Farnese Hercules, 205 
Fava, 65 

Federated Malay States, cassitcritc 

from, 112 
Feel of gems, 63 
Fell, Charles, 249 
Feldspar, 167, 174 

cleavage of, 60 

composition of, 12 

jadelike, 200 

orthoclase, crystal of, 22 

plagioclase, crystal of, 22 

resemblance to scapolite, 1 17 

with diopside, 119 
Feldspathoid group, 182 
Fibrolite, 160 
Fibrous gems, luster of, 31 
Figure stone, 201 
File, steel, hardness of, 59 
Filter, ultraviolet, 278, 279, 280, 

281, 282 

Finger nail, hardness of, 59 
Fire, 37, 38 

misuse of term, 225 
Fire opal, 224, 228 
Fisheries, pearl, 237 
Flat surface, polishing, 74 
Flaws, caused by heat, 64 

in diamond, 91 
Flcencr, Frank L., 285 
Flint, 223 
Flint glass, 260 
Florentine diamond, 9? 
Florida, carnelian from, 213 
Flower agate, 217 
Fluorescence, 51, 1 M, 141, 270, 
271, 272, 273, 274, 275, 276, 
277, 278, 279, 280, 282 

of amber, 242 

of synthetic emerald, 257 
Fluorescent equipment, 278 
Fluorides, 12 


Fluorite, 112 
composition of, 12 
crystallization of, 19, 144 
fluorescence of, 271, 275, 279 
^luorspar, 113 
-oil, 261, 263 
Cool's gold, 164 

in lapis lazuli, 183 
; orni, crystal, 16, 17, 18, 19, 59 
formation of gems, 65 
fortification agate, 218, 220 
Fossil amber, 244 
Fossil coral, 239 
France, diamond die industry in, 


gems from, 158, 184, 197 
manufacture of synthetic corun- 
dum in, 255 
Fracture, 55, 60 
Franklinite, 141, 274 
French Academy of Sciences, 125 
French Africa, diamond from, 91 
French Alps, axinite from, 158 
Fremy, Edmond, 249 
Frequency control, rock crystal 

used for, 207 
Frondel, Clifford, 74, 164 
Fundy, Bay of, pearl essence from, 


Fused quartz, 260 
Fused silica tube, 280 

Garnet, 141 

almandite, absorption spectrum 
in, 44 

in composite gems, 264 
andradite, dispersion in, 38 

luster of, 31 
asterisrn in, 50 
Bohemian, 143 
composition of, 12 

Garnet, crystallization of, 19, 

demantoid, absence of dichroism 
in, 46 

dichroism in, absence of, 46 

effect of acid on, 13 

green, 118 

isomorphism in, 14 

jadelike, 200 

occurrence of, 65 

origin of, 67 

star, 50 

synthetic, 143 

with diamond, 65 

with idocrase, 195 

with staurolite, 197 
Garnet doublet, 263 
Garnet triplet, 263 
Gaudin, Marc, 249 
Gel, silica, 20} 
Gem cutting, books on, 284 
Gem of the Jungle sapphire, 103 
Gemmological Association of 

Australia, 4 
Gemmological Association of 

Great Britain, 4 
Genrnwlogist, The, 286 
Gemological Institute of America, 


Gemological movement, 4 
Gemology, growth of, 4 
Ge?f?s and Gem Materials^ 283 
Gews and Gewology, 285 
Gemstoncs, 36, 55, 283 
Gein Testing, 284 
Gem testing, books on, 284 
Geode, 68 

Geologic occurrence of gems, 65 
Georgia, staurolite from, 197 
Germany, agate cut in, 219 

dyeing of agate in, 219, 220 


Germany, gems from, 197, 210, 
214, 219; see also Baltic Sea, 
Bavaria, East Prussia, Prus- 
sia, Samland, Saxony, Si- 

manufacture of synthetic corun- 
dum in, 255 
Germicidal lamp, 282 
Geyserite, 229 

Geysers, opal deposited by, 229 
Gilbert and Sullivan, 259 
Girdle, 58, 73 
Glaciers, action of, 67 
Glass, 260 

absence of dichroism in, 46 

hardness of, 59 

in opal doublet, 228 

luster of, 31 

natural, 8, 202, 229 
Glass imitations, cause of dulling 
of, 12 

hardness of, 57 
Glossary, gem, book, 284 
Goethite, in sagenite, 209 
Golconda, 89 

Gold Coast, gems from, 88, 110 
Gold quartz, 209 
Goldstone, 180, 206, 261 
Goshenite, 131 
Grain, 59, 86 

pearl, 52 
Graphite, 92 

polymorphism of, 15 
Gravel, 223 
Gravel deposits, 67, 68; see also 


Grease, effect of, on gems, 13 
Grease table, diamond, 80, 81 
Greasy luster, 31 

Great Britain, gems from, 157; sec 
also England, Ireland, Scot- 
land, Wales 

Greece, gems from, 168, 231 

Green garnet, 118 

Greenland, gems from, 12?, 144 

Greenstone, 191 

Griqualand West, South Africa, 
tiger's-eye in, 210 

Grossularite garnet, 143, 146 

Guardian angels, gems of the, 5 

Gulf of Mannar, pearl from, 237 

Gulf of Mexico, pearl from, 238 

Gypsum, 198 
crystallization of, 22 
satin spar, luster of, 31 

Habit, 16, 59 

Halides, 12 

Hamlin, Elijah, 126 

Hand lens, 27 

Handbook of dew Identification, 


Hard gems, polish on, 30 
Hardebank, 77 
I lardness, 55, 60 

scale of, 56 

table, 58 

Hardness points, 59 
Harlequin opal, 226 
Haiiy, Abbe, 15 
Hauynite, 182 
Hawk's-eye, 210, 211 

chatoyancy in, 50 
Head of the Dog Sirius, 145 
Heat, 63 

electricity due to, 62 

treating gems with, 266 
Heavy liquids, 53 
Heberden, Dr., 125 
Heliodor, 131, 137 


Heliotrope, 215 
Hematite, 164, 166 

crystallization of, 21 

in aventurine, 206 

in suns tone, 180 

luster of, 31 

scientific, 262 

specific gravity of, 55 

streak of, 30 
Hemimorphite, 167 
Henderson, Edward P., 114 
Henderson, Randall, 286 
Henry II, 132 
Henry V, 105 
I ferculaneuin, emerald used in, 


Hcrkimcr diamond, 209 
Herschcl, Sir John, 271 
Hcssonite, 146 
Hexagonal crystals, 18, 20 
Hexagonal gems, effect of light 

on, 39, 40 

Hexagonal system, 17, 20, 21 
Hidden, William K., 121 
Hiddenite, 121 

crystallization of, 21 
I figh-potcntial spark, 279 
High priest's breastplate, 5 
High zircon, 148, 149 
Hills of Precious Stones,. Siam, 

ruby from, 101 
Holmes, Ezckiel, 126 
Honduras, carved jade from, 187 

white opal from, 226 
Hope collection, 109 
Hope diamond, 93, 94 
Hot bulb, 282 
Hungarian opal, 226 
Hyacinth, 150, 151 
Hyacinth-garnet, 146 
Hyalite, 229 

Hyderabad, Golconda, 89 

Hydrocarbons, 12 

Hydrochloric acid, effect of, on 

gems, 13 
Hydrogen sulfide, effect of, on 

glass imitations, 12 
Hydrophane, 229 
Hypersthene, 118 

Ice, crystallization of, 20 
Iceland, obsidian from, 231 
Iceland spar, 45 
Identification, of composite gems, 


of gems, 18, 19 
by absorption spectrum, 42, 4 ^ 
by chemical tests, 2^ 
by color, 29 
by crystal form, 10 
by double refraction, 40, 48 
by hardness, 57 
by heat tests, 64 
by luster, 31 
by polarization, 48 
by refraction, 32 
by refractive index, 33, 34, ^ 
of synthetic corundum, 253 
of synthetic emerald, 257 
optical instruments for, 43 
Idiochromatic gem, 28 
Idocrase, 194 
crystallization of, 19, 20 
jadelike, 200 
Igmerald, 257 
Igneous rocks, 66, 67 
111am, 152 

Illinois, fluorite from, 113 
Imitation emerald, flaws in, 132 
Imitation gems, 8, 247, 259 
Imitation opal, 114 


Imitations, glass, cause of dulling 

of, 12 

scratching of, 57 
Imitative shapes, 23 

of opal, 225 
Impact, 55 

Imperial Guard, Russian, 108 
Imperial jade, 189 
Imperial topaz, 156 
Impurities, effect of, on lumi- 
nescence, 273 

Incas, emerald used by, 133 
Inclusions, minor properties due 

to, 64 
Index, refractive, see Refractive 


India, aquamarine used in, 134 
coral used in, 238 
diamond cutting in, 86 
gems from, 87, 89, 104, 126, 145, 
155, 161, 206, 210, 213, 215, 
217, 276; see also Burma, 
Ceylon, Kashmir 
itacolumitc in, 223 
Indians, American, jet used by, 


turquoise used by, 172, 173 
Indicators, 53 
Indicolite, 128 
Indo-China, gems from, 101, 104, 

151, 152 

Industrial diamond, 95 
Industrial Distributors (1946), 

Ltd., 96 

Industrial use, of garnet, 143 
of quartz, 16, 63, 223 
of synthetic corundum, 254 
of synthetic diamond, 258 
of synthetic spinel, 256 
Inhibitor, 274 
Insects, in amber, 241, 242 

Instruments, for analyzing color, 


optical, 29, 43 
Intaglio, 3 

hematite, 30, 166 

Interference of light, 50, 175, 180 
in opal, 224, 225 
in pearl, 236 
Intermediate zircon, 148 
lolitc, 117 
Ions, 16, 55, 141 
Iran, turquoise from, 172 
Ireland, emerald associated with, 


gems from, 238, 240 
Iris agate, 218 
Iris quartz, 209 
Iron arc, 280 

Iron Cross of Lombardy, 132 
Iron markings, 23 
Isle Royale National Park, Michi- 
gan, prehnite from, 184 
Isometric crystals, 18, 19 
Isometric gems, absence of dichro- 

ism in, 45 

effect of light on, 39, 40, 41 
polarization in, 48 
Isometric system, 17, 19 
Isomorphism, 14, 141, 143, 183 

in feldspar, 179 
Itacolumite, 223 

Italy, gems from, 119, 147, 195, 
199, 239; see also Elba, 
Mediterranean Sea, Medi- 
terranean islands, Mount 
Vesuvius, Piedmont Prov- 
ince, Sicily 

Jacinth, 103, 150, 151 
Jacinth-garnet, 146 


Jade, 167, 184 

color in, importance of, 26 

composition of, 12 

fluorescence of, 276 

in Central America, 119 

luster of, 31 

origin of, 67 

resemblance to amazonstone, 178 

substitutes, feel of, 63 

tomb, 188 

toughness of, 62 

Jade quarries, occurrence of, 67 
Jadeite, 118, 185, 188 

with diopside, 119 
Jadelike minerals, 200 
Japan, gems from, 206, 208, 238, 
240, 276 

pearl culture in, 267 
Jargoon, 150 
Jasper, 213, 215 

imitated in lapis lazuli, 221 
Jasper opal, 229 
Jasperized wood, 222 
Jet, 8, 233, 244 

composition of, 12 

heat test for, 64 

imitation, 261 

origin of, 69 
Jet rock, 245 
Jewel, 6 

Jeweler's loupe, 27 
Jig, 80 
Job, 138 

' Jonker diamond, 92 
Jubilee diamond, 93 

Kafirs, loading blue ground, 79 

Kandy, king of, 109 

Kaolin, 174 

Kao-tsung, Emperor, 188 

Karat, 51 

Kashmir, sapphire from, 104 
Kathe district, Burma, ruby from, 


Kauri gum, 244 
Kentucky, fluorite from, 113 
Kenya, East Africa, kyanite from, 


Keystone cut, 73 
Kimberley diamond mine, 88 

enstatite from, 118 

zircon from, 153 
Kimberlite, 66, 97 
King-Cut diamond, 73 
Knife blade, hardness of, 59 
Koh-i-nur diamond, 93 
Kraus, Edward H., 283 
Kunz, George F., 122 
Kunzite, 121 

crystallization of, 21, 120 

cleavage of, 60 

dichroism in, 44 

fluorescence of, 279 

phosphorescence of, 275 
Kyanite, 160 

crystallization of, 22 

hardness of, 57 

polymorphism of, 15 

with staurolite, 197 

Labrador, labradorite in, 181 

Labradorite, 179, 180 
crystallization of, 22 
interference of light in, 51 

Lamp, germicidal, 282 
mercury vapor, 280, 281 

Landscape agate, 217 

Laocoon group, 205 

Lapidary, amateur, 202, 213 

Lapidary apparatus, 74 

Lapidary Journal, The, 286 


Lapidary treatment of gems, 70, 

71, 73, 74 
Lapis, 183 
Lapis lazuli, 8, 103, 167, 181, 182 

color in, importance of, 26 

effect of acid on, 13, 14 

imitated in jasper, 221 

origin of, 67 
Lattice, 16 
Lava, 65, 66 

gems in, 65, 66, 184, 229 
Lazurite, 183 
Leakage of light, 33 
Lechosos opal, 226 
Lens, hand, 27 
Lepidolite, 130 
Libyan Desert, silica-glass from, 


Lichtenburg, diamond from, 87 
Liddicoat, Richard C, Jr., 284 
Lifting of gems, 55 
Light, absorption of, 26, 30 

bending of, 32 

composition of, 26 

diffraction of, in pearl, 236 

interference of, 50, 175, 180 
in opal, 224, 225 
in pearl, 236 

leakage of, 33 

speed of, 32 

ultraviolet, see Ultraviolet light 
Lightning, fluorescence in, 279 
Lightning Ridge opal field, New 

South Wales, 227 
Lignite, 244 
Limonite, 174 
Linde Air Products Company, 250, 

Little Namaqualand, diamond 

from, 87 
Lombardy, Iron Cross of, 132 

Loupe, jeweler's, 27 
Low zircon, 148, 149, 150 
Lozenge cut, 73 
Luminescence, 51, 270 
Luminescent gems, 270 
Lure of gems, 1 
Luster, 30, 55 
metallic, 164 

Macedonians, pearl fishing by, 237 

Madagascar, gems from, 116, 119, 

120, 121, 122, 126, 127, 136, 

137, 177, 178, 179, 180, 207, 


Magazines, selected, 285 
Magma, 66 

Magna-Cut diamond, 73 
Magnifier, utility, 27 
Magnifying instruments, 27 
Maine, gems from, 116, 122, 125, 
136, 146, 181 

pearl essence from, 262 
Malachite, 168, 171, 193 

banded, 169 

crystals of, 170 
Manganese markings, 23 
Mantle, 234, 235, 267 
Manufactured chemicals, distin- 
guished from minerals, 6 
Maoris, nephrite used by, 192 
Marble, 198 

dendrites on, 23 

marking in, 23 
Marcasite, 166 
Marco Polo, 107, 133, 183 
Mark Antony, 224 
Marker, diamond, 86 
Marketing diamond, 87, 90 
Marking diamond, 82 
Marlborough collection, 109, 145 
Marquise cut, 73 


Massachusetts, gems from, 154, 


Massive gems, 23 
Matura diamond, 150 
Mayan jade carving, 187 
Mclntyre, O. O., 133 
McLean, Evalyn Walsh, 94 
Mechanical device, for faceting, 


Medical use of gems, 3 
Mediterranean Sea, coral from, 

238, 240 
Mediterranean islands, obsidian 

from, 231 
Meerschaum, 199 
Melanite, 147 
Meleagrina, 237 
Mercury vapor lamp, 280, 281 
Metallic gems, 164 
Metallic luster, 31, 164 
Metamorphic rocks, 66, 67 
Meteorites, 65, 69 

diamond in, 69, 98 

olivine in, 69, 139 
Methylene iodide, 53 
Metric carat, 51, 52 
Mexican jade, 13 
Mexico, carved jade from, 187 

gems from, 111, 112, 116, 119, 
146, 189, 228, 231 

obsidian blades from, 230 
Mica, in aventurine, 206 
Mica, Mount, Maine, tourmaline 

from, 126 
Michigan, gems from, 154, 184, 

Microcline, 175, 178, 180 

crystallization of, 22 
Microperthite, 177 
Microscope, petrographic, 43 

Middle East, turquoise used in, 


Milky quartz, 209 
Minas Geraes, Brazil, gems from, 

115, 136, 137 

Miniatures in moss agate, 72 
Mineral, definition of, 6 
Mineralogist Magazine, The, 285 
Minerals used as gems, 6, 11 
Mineral species used as gems, 7, 9 
Mining, of amber, 241 

of diamond, 77, 79 

of gems, 67 
Minor properties, 64 
Mississippi River, pearl from, 238 
Missouri, moss agate from, 216 
Mocha stone, 217 
Mogok Stone Tract, Burma, ruby 

from, 100 

Mohs, Frederich, 56 
Mohs' scale of hardness, 56 
Moissan, Henri, 258 
Moldavia, Czechoslovakia, molda- 

vite from, 231 
Moldavitc, 231 
Mollusk, 234, 235, 237, 267 
Monoclinic crystals, 18, 22 
Monoclinic gems, dichroism in, 

effect of light on, 39, 40 
Monoclinic system, 17, 21 
Montana, gems from, 68, 103, 104, 

206, 217, 276 

Moon of Boroda diamond, 94 
Moonstone, 177, 178, 180 

crystallization of, 21 

effect of grease on, 13 

imitation, 260 

in pegmatite, 67 

interference of light in, 51 


Moonstone, pink, 116, 178 

quartz, 178 

scapolite, 116, 178 
Morgan, J. Pierpont, 136 
Morganite, 131, 136 
Morion, 212 
Morse, Henry, 73 
Moss agate, 216 

miniatures in, 72 
Moss opal, 229 
Mother-of-pearl, 236, 237, 267, 269, 

Mount Antcro, Colorado, gems 

from, 135, 136, 140 
Mount Mica, Maine, tourmaline 

from, 126 
Mount Vesuvius, gems from, 117, 

181, 194, 195 

Multi-Facet diamond, 73 
Multiple oxides, 12 
Mussel, pearl, 237, 238, 266 
Mutton-fat jade, 189 
Muzo, Colombia, emerald from, 

Mystical attributes of gems, 3 

Nacre, 235, 236, 266, 267 

Napoleon, 205 

Nassak diamond, 93 

National Association of Gold- 
smiths, 4 

National Bureau of Standards, 93, 

Natural glass, 8, 202, 229 

Navajos, turquoise used by, 173 

Necklace, 1, 2 

Nephrite, 185, 190 

Neptunite, 123 

Netherlands, diamond cutting i:i, 
94, 95 

Nevada, fluorescent opal from, 276 

gems from, 173, 197, 227, 231 
New England, gems from, 158; see 

also wawes of states 
New Guinea, pearl from, 238 
New Jagersfontein diamond mine, 

New Jersey, gems from, 141, 154, 

184, 193, 273 

New Jersey Zinc Company, 274 
New Mexico, gems from, 139, 144, 

168, 173, 194 
New South Wales, Australia, gems 

from, 89, 153, 193, 226, 227 
Newfoundland, labradorite from, 


Newton, Sir Isaac, 26, 28, 37 
New York, gems from, 106, 119, 

129, 143, 145, 199, 209, 223 
New York City, diamond cutting 

in, 95 

garnet from, 143, 145 
New Zealand, gems from, 191, 

192, 200, 244 
jade used in, 186 
Nicol prism, 48 
Niggerhead, 127 
Niningcr, Harvey H., 98, 259 
Noncrystalline gems, 16 
Nonius, 224 
Nonmetallic gems, 167 
Norway, gems from, 153, 166, 179, 

180, 195 
Noselite, 183 

Notching diamond, 82, 86 
North Carolina, gems from, 121, 

122, 134, 136, 144, 161, 197, 


itacolumite in, 223 
North Italian Mountain, Colorado, 

lapis lazuli from, 184 


Obsidian, 8, 229 

fracture of, 61 

origin of, 66 
Occurrence of gems, 65 
Octahedron, 91, 105 
Odontolite, 174 
Odor of amber, 244 
Office of Technical Services, 
Oil of turpentine, effect of, 

coral, 13 

Oily surface, luster of, 31 
Oligoclase, 179, 180 

moonstone, 178 
Olivine, 138, 147, 199 

composition of, 12 

crystallization of, 21 

double refraction in, 40 

in meteorites, 69 

isomorphism in, 14 

occurrence of, 65, 69 
Olivine series, 139 
Ontario, Canada, gems from, 

119, 181 

Onyx, 198, 221, 222 
Opal, 202, 203, 222, 224 

color in, importance of, 26 

effect of drying on, 64 

fluorescence of, 275, 279 

formed by springs, 69 

imitation, 114, 260 

in geode, 68 

interference of light in, 50 

specific gravity test for, 53 
Opal doublet, 228, 263, 264 
Opalized wood, 222 
Opal-matrix, 228 
Opaque gems, cause of color 

importance of color in, 26 

scratching of, 56 
Operculum, 110 




Optic axis, 40, 41, 46, 48, 253 
Optical density, 32 
Optical instruments, 29, 43 
Optical properties, 24, 25, 51, 64 

related to crystallization, 18 
Optics, 25 

Oregon, gems from, 214, 217, 218 
Organic gems, 8, 233 

occurrence of, 69 
Orient of pearl, 236 
Oriental amethyst, 99 
Oriental emerald, 99 
Origin of gems, 65 
Orloff diamond, 93 
Ornamental gems, imitation, 262 
Ornamental stones, 198 
Orthoclase, 175, 177, 180 

crystallization of, 21, 22 
Orthorhombic crystals, 18, 21 
Orthorhombic gems, dichroism in, 

effect of light on, 39, 40 
Orthorhombic system, 17, 21 
Oxides, 12 

Oxygen, abundance of, in gems, 12 
Oyster, pearl, 237 

Pacific Ocean, gems from, 238, 


Padparadschah, 103, 252 
Pagoda stone, 201 
Palache, Charles, 74, 164 
Palestine, diamond cutting in, 95 
Parting, 55, 60 
Paste, 246, 261 
Patagonia, petrified wood from, 

Pearl, 8, 233 

black, substitute for, 166 

composition of, 12 

cultured, 238, 266 


Pearl, effect of acid on, 13 

effect of grease on, 13 

effect of perspiration on, 13 

effect of vinegar on, 13 

fluorescence of, 276 

imitation, 262 

luster of, 31 

pierced for stringing, 70 

specific gravity test for, 55 

unit of weight for, 52 
Pearl essence, 262 
Pearl grain, 52 
Pearl mussel, 237 
Pearl oyster, 237 
Pearly luster, 31 
Pectolite, 200 
Pedro the Cruel, 105 
Pegmatite, 66, 67 

gems in, 115, 120, 135, 142, 156, 


Pendeloque cut, 73 
Pennsylvania, garnet from, 142 
Peridot, 138, 139; see also Olivine 

Brazilian, 128 

Ceylonese, 128 

confusion of name with topaz, 


Peristeritc, 180 

Persia, turquoise used in, 172 
Persian Gulf, gems from, 237, 240, 


Perspiration, effect of, on pearl, 13 
Peruvian emerald, 133 
Peruzzi, Vincenti, 71 
Petrified Forest National Monu- 
ment, Arizona, 223 
Petrified wood, 14, 222 
Petrographic microscope, 43 
Phantom crystal, 15 
Phenakite, 140 

crystallization of, 21 

Phoenicians, amber marketed by, 


Phosphates, 12, 116 
Phosphorescence, 51, 270, 271, 272, 

273, 274, 275 

Physical properties, 25, 51 
Physics, optics as a branch of, 25 
Picotite, 106 
Piedmont Province, Italy, gems 

from, 119, 195 
Piezoelectricity, 62 
Pigeon's blood ruby, 100 
Pikes Peak region, Colorado, 
gems from, 153, 176, 179, 

Pinite, 201 

Pink moonstone, 116, 178 
Pink sapphire, 101 
Pink spinel, fluorescence of, 275 
Pinking, of topaz, 155, 265 
Pinus succinifera, 240 
Pipe, diamond, 77, 87 

mines, 88 
Pistacite, 148 
Placers, 67, 68 

gems in, 87, 108, 156, 177 
Plagioclase, 175, 177, 178, 179 

crystallization of, 22 
Plant structure, 222 
Plasma, 215 
Plastics, 261 

heat test for, 64 

salt water test for, 53 
Plato, 145 
Play of color, in feldspar, 175, 180 

in opal, 224, 225, 226, 228, 229 
Pleonaste, 106 
Pliny, 182, 204, 224 
Plume agate, 217 
Point, 52 

diamond, 71 


Polar electricity, 62 
Polarity, 128 
Polarization, 47, 130 
Polarized light, 47, 48, 49 
Polaroid Film, 47, 48, 49 
Polishing, diamond, 31, 86 
with electric arc, 97 

flat surface, 74 

slab, 74 

Polymorphism, 15 
Polyp, 239 

Pompeii, emerald used in, 132 
Pope, Alexander, 242 
Porcelain, 262 
Porous gems, specific gravity test 

for, 53 

Portability of gems, 8 
Portugal, Braganza diamond in, 

Portuguese Africa, diamond from, 


Potash feldspar, 175, 178 
Pough, Frederick H., 114 
Prase, 214 
Prase opal, 229 
Precious garnet, 145 
Precious opal, 226 
Precipitates, chemical, 67 
Prehnite, 184 

jadelike, 200 

Premier diamond mine, 88 
Pressure, electricity due to, 62 
Prism, 19 
Properties of gems, 10, 25 

chemical, 25 

optical, 24, 25, 51, 64 
related to crystallization, 18 

physical, 25, 51 

Prussia, East, amber from, 241 
Pseudomorphism, 14, 23 

in opal, 225, 228 

Pulsator, 80 

Punch Jones diamond, 80 

Pyramid, 19 

Pyrite, 164 

composition of, 12 

crystallization of, 19, 20, 165 

in lapis lazuli, 183 

luster of, 31 

streak of, 30 
Pyritohedron, 165 
Pyroelectricity, 62 
Pyrope, 143, 144 

occurrence of, 65 
Pyrophyllite, 201 

Pyroxene group, 118, 119, 121, 
189, 190, 193 

Quartz, 202, 203, 285 
asterism in, 50 
birefringence in, 41 
cat's-eye, chatoyancy in, 50, 210 
composition of, 12 
confused with beryl, 131 
confused with phenakitc, 140 
cryptocrystalline, 203 
crystalline, 203 
crystallization of, 21, 204 
fluorescence of, 277 
fracture of, 61 
fused, 260 
gold, 209 
hardness of, 56 
in composite gems, 264 
in geode, 68 
in igneous rocks, 66 
in petrified wood, 14 
jadelike, 200 
milky, 209 
moonstone, 178 
occurrence of, 65 
rainbow, 209 


Quartz, resemblance to cordierite, 


rose, 211 
asterism in, 50 
in pegmatite, 67 
smoky, 211 

in pegmatite, 67 
star, 50 
" treated, 266 
use of, 16, 63, 223 
Quartz cat's-eye, 210 
Quartz Family Minerals, 285 
Quartz vein, 67 
Quartzite, 223 

Quebec, Canada, gems from, 181 
Queen Charlotte, 205 
Queen Victoria, 105, 228 
Queensland, Australia, black opal 

from, 227 
Quick, Lclande, 286 

Radioactivity, in heliodor, 137 

in opal, 276 

in ruby, 102 

in smoky quartz, 211 

in zircon, 149 

luminescence due to, 270 

treating gems with, 265 
Rainbow, 37 
Rainbow quartz, 209 
Rainbow Ridge opal mine, Ne- 
vada, 227 

Rarity of gems, 8 
Reading, selected, 283 
Recognizing gems, 6 
Reconstructed amber, 244 
Reconstructed gems, 248 
Red spinel, fluorescence of, 275 
References, 283 
Reflection, 30 

total internal, 33 

Refraction, 30, 32 

Refractive index, 32, 33, 35, 38, 
39, 40, 41, 44 

determination of, 33, 34, 35 

table, 36 

Refractive power, 31 
Rcfractometer, 34, 35, 41 
Religious attributes of gems, 3 
Rcpolishing gems, 56 
Resin, amber formed from, 240 
Resin opal, 229 
Resinous luster, 31 
Resonance of jade, 189 
Rhinestones, 261 
Rhodes, Cecil, 77 

Rhodesia, gems from, 101, 110, 170 
Rhodolite, 144 
Rhodonite, 192 

crystallization of, 22 
Ribbon jasper, 215 
River pearl, 238 
Robin's-egg turquoise, 173 
Rock, definition of, 7 

distinguished from mineral, 6 

occurrence of gems in, 65 

used as gems, 7 
Rock crystal, 207, 209 

crystallization of, 21 

use of name, 16 
Rocks and Minerals, 285 
Rod, synthetic corundum, 254, 255 
Roebling opal, 227 
Rome, amethyst used in, 205 

aquamarine used in, 134 

emerald used in, 224 

manufacture of pearl in, 246 

opal used in, 224, 226 
Rose cut, 71 
Rose opal, 229 
Rose quartz, 211 

asterism in, 50 


Rose quartz, in pegmatite, 67 

star, 50 

Rosin jack, 111 
Rospoli sapphire, 103 
Rotary washing pan, diamond, 81 
Rough gems, testing, for hardness, 


Rounding diamond, 84 
Rozircon, 248 
Rubellite, 128, 130 
Rubicelle, 105 
Ruby, 98, 100; see also Corundum 

absorption spectrum in, 43 

Arizona, 144 

asterism in, 50 

Cape, 144 

cause of color in, 28 

Colorado, 144 

crystallization of, 20 

dichroism in, 46 

fluorescence of, 275 

orientation of, in cutting, 50 

parting of, 60 

relationship to sapphire, 29 

star, 102 

synthetic, 248, 250 

fluorescence of, 276 
Rumanian amber, 243 
Rumanite, 243 
Ruskin, John, 70 

quoted, 12, 69, 127, 128, 224 
Russia, gems from, 89, 126, 137, 
152, 157, 170, 179, 181, 193, 
206; see also Siberia, Ural 

jasper used in, 216 

malachite used in, 168 

rhodonite used in, 192 
Russian crown jewels, 205 
Rutile, in sagenite, 209 

Sagenite, 209 

St. Gotthard Mountains, adularia 

from, 178 

St. John's island, peridot from, 138 
Salt, table, 19 
Salt water, test for amber, 53, 243 

test for bakelite, 243 

test for glass, 243 

test for plastics, 243 
Samland, East Prussia, amber from, 

Sand, 223, 260 

in air, 46 

Sand dunes, olivine in, 139 
Sandstone, 223 
Saponite, 201 

Sapphire, 98, 102; see also Corun- 

asterism in, 50 

Brazilian, 128 

crystallization of, 20, 99 

dichroism in, 46 

in Montana, 68 

of the Bible, 182 

parting of, 60 

pink, 101 

relationship to ruby, 29 

star, 102 

synthetic, 248, 250 
Sard, 214 
Sardonyx, 222 
Satellite, 65 
Satin spar, 199 

crystallization of, 22 

luster of, 31 
Saussurite, 195 
Sawing diamond, 83 

with electric arc, 97 
Sawyer, diamond, 86 
Saxony, Germany, gems from, 171, 


Scale of hardness, 57 
Scapolite, 116 

crystallization of, 19 

moonstone, 116, 178 
Scarab, 2 
Scenic agate, 217 
Schiller, 119 
Schillerization, 177 
Schorl, 128, 130 
Scientific hematite, 262 
Scotland, gems from, 197, 212, 238 
Scott, Sir Walter, 228 
Scratching, 56 

resistance to, 61 
Sculpture, gem, 163 
Seal, 2, 163, 208, 213 
Seaweed agate, 217 
Sedimentary rocks, 66, 67 

diamond in, 87 
Seed pearl, 236 
Sepiolite, 199 
Selected reading, 283 
Semiprecious, obsolete use of 

word, 9 
Serpentine, 199 

Siam, gems from, 101, 104, 106, 

zircon treated in, 152 
Siamese zircon, 152 
Siberia, gems from, 126, 134, 136, 
157, 159, 180, 183, 191, 195, 
206, 216; see also Ural 
Siberite, 128 
Sicilian amber, 242 
Sicily, agate from, 219 
Sierra Leone, diamond from, 88, 


Signet, 3 

Silesia, gems from, 192, 214 
Silica gel, 203 

Silica-glass, 8, 231 

Silicates, 12 

Siliceous sinter, 229 

Silicified wood, 222 

Silicon, abundance of, in gems, 12 

Silky luster, 31 

Silliman, Benjamin, 160 

Sillimanite, 159 

crystallization of, 21 

jadelike, 200 

polymorphism of, 15 

with staurolite, 197 
Simetite, 242 
Simulated gems, 261 
Sinai Peninsula, Egypt, turquoise 

from, 172 

Single refraction, 48 
Singly refractive gems, 35 

polarization in, 48 
Sinter, siliceous, 229 
Shellfish, 234, 235 
Shell -like fracture, 61 
Shipley, Robert M., 4, 284, 286 
Skin, of pearl, 236 

on diamond, 86 

on moss agate, 216 
Skip, 77 

Slab, polishing, 74 
Slawson, Chester B., 283 
Smith, George F. Herbert, 36, 55. 


Smithson, James, 167 
Smithsonian Institution, 167 
Smithsonite, 167 

banded, 168 

composition of, 12 
Smoky quartz, 211 

in pegmatite, 67 

treated, 266 
Snow, crystallization of, 20 


Soapstone, 200, 201 

feel of, 63 

Soda-lime feldspar, 179 
Sodalite, 181, 183 
Sodic plagioclase, 180 
Sorting diamond, 85 
Soude emerald, 263, 264 
South Africa, gems from, 118, 119, 
139, 144, 153, 170, 211, 274 
South African jade, 146 
South America, gems from, 96, 
116, 238; see also names of 
countries, Patagonia 
South Australia, Australia, gems 

from, 170, 226 

South Carolina, topaz from, 158 
South Dakota, gems from, 120, 211, 

219, 223 
South Pacific Ocean, pearl from, 

South-West Africa, gems from, 

113, 137, 168, 170, 211 
Space-group, 17 
Spain, gems from, 111, 159, 168, 

212, 245 

Spanish emerald, 133 
Spark, high-potential, 279 
Specific gravity, 51 
Spectroscope, 29, 42, 43, 44, 145 
Spectrum, 26, 28, 37, 42, 271 

absorption, 42, 145 
Spessartite, 143, 146 
Sphalerite, 111, 167 

crystallization of, 19 

dispersion in, 38 
Sphene, 161 

crystallization of, 21, 22 

dispersion in, 38 

double refraction in, 40 

luster of, 31 

Sphere, 71, 213 

rock crystal, 207, 218 
Spinel, 104 

absence of dichroism in, 46 

composition of, 12 

crystallization of, 19, 106 

fluorescence of, 275 

isomorphism in, 14 

synthetic, 104, 108, 248, 253, 255, 


fluorescence of, 277 
Splintery fracture, 61 
Spodumene, 118, 120, 190 

crystallization of, 21 

fluorescence of, 279 

in pegmatite, 67 

kunzite, cleavage of, 60 
dichroism in, 44 

phosphorescence of, 275 
Springs, gems formed by, 65, 69, 

225, 229 

Stainless steel, 262 
Star garnet, 50 
Star of Estc diamond, 93 
Star of South Africa diamond, 176 
Star rose quartz, 50 
Star ruby, 102 

synthetic, 250 
Star sapphire, 102, 103 

synthetic, 250 
Starlite, 150, 151, 266 
Star stones, 50 
Staurolite, 159, 195 

crystallization of, 21, 196 

pierced for hanging, 70 

twin crystal of, 17 
Steatite, 201 

feel of, 63 
Steel, stainless, 262 
Steel file, hardness of, 59 
Step cut, 73 


Stokes, Sir George G., 271, 279 

Stokes' law, 272 

Strass, 261 

Streak, 29 

Streams, action of, 67 

Structure, atomic, 7, 16, 17, 18, 2"?, 

24, 294 

of diamond, 7, 57 
of feldspar, 176 
of obsidian, 231 
of opal, 225 
of sphalerite, 111 
of synthetic corundum, 253 
of synthetic spinel, 256 
minor properties due to, 64 
related to crystal form, 7 
cryptocrystalline, in chalcedony, 

212 ' 

crystal, 15, 16, 17, 18 
of pearl, 235, 269 
plant, 222 
Stuarts Range opal field, South 

Australia, 226 
Subadamantine luster, 31 
Succinite, 242 
Suite of minerals, 65 
Sulfides, 12 

Sulu Sea, pearl from, 238 
Sumatra, cassiterite from, 112 
Sung catalogue of jade, 188 
Sunlight, fluorescence in, 279 
Sunshine test for double refrac- 
tion, 40 
Sunstone, 180 
Superior, Lake, region, prehnite 

from, 184 

Superstitions, related to color, 25 
Sweden, gems from, 166, 193 
Swiss Alps, calif ornite from, 195 
Switzerland, diamond die indus- 
try in, 96 

Switzerland, gems from, 113, 147, 
161, 162, 177, 178, 195, 197, 

jade used in, 188 
manufacture of reconstructed 

ruby in, 249 

manufacture of synthetic corun- 
dum in, 255 
nephrite used in, 192 
Symbolism, related to color, 25 

of gems, 3 
Symmetry, 17 
Syndicate, Diamond, 90 
Synthetic beryl, H4, 256, 260, 264 
Synthetic corundum, 108, 249, 264 
Synthetic diamond, 258 
Synthetic emerald, 134, 256, 260, 


fluorescence of, 277 
Synthetic garnet, 143 
Synthetic gems, 8, 16, 246, 247, 248 
Synthetic ruby, fluorescence of, 

Synthetic spinel, 104, 108, 255, 264 

fluorescence of, 277 
System, crystal, 17, 18 

Table cut, 71 

Tailings dump, diamond mine, 79, 


Talc, 201 
Tanganyika Territory, ^ems from, 

88, 140, 177 
Tasmania, Australia, axinite from, 


Tektite, 8, 231 
Tenacity, 55, 61 
Tertiary Period, amber in, 240 
Test, card, for double refraction, 

Testing, gem, books on, 284 


Tests, chemical, 25 

heat, 64 

Tetragonal crystals, 18, 20 
Tetragonal gems, effect of light 

on, 39, 40 

Tetragonal system, 17, 19 
Thermoluminescence, 275 
Thomas Mountains, Utah, topaz 

from, 157 
Thulite, 195 
Thunder egg, 217, 218 
Tibet, turquoise used in, 172 
Tiffany diamond, 93 
Tiger's-eye, 210 

chatoyancy in, 50 
Tin ore, with topaz, 156 
Tin-stone, 112 

Tirol, gems from, 119, 134, 195 
Titanite, 161, 162 
Tomb jade, 188 
Tongs, tourmaline, 130 
Topaz, 155 

brittleness of, 61 

cleavage of, 60 

composition of, 12 

critical angle in, 33, 34 

crystallization of, 21, 157 

electricity in, 62 

feel of, 63 

heated, 265 

isomorphism in, 14 

refractive index of, 33 

relationship to danburite, H7 

resemblance to citrine, 206 
Topazolite, 147 
Total internal reflection, 33 
Touch, 63 
Toughness, 55, 61 
Tourmaline, 124 

composition of, 12 

crystallization of, 20, 21, 129 

Tourmaline, dichroism in, 44 

electricity in, 62, 63 

in sagenite, 209 

occurrence of, 65 

orientation of tourmaline in cut- 
ting, 50 

polarization 'in, 48 
^with idocrase, 195 

with staurolite, 197 
Tourmaline cat's-eye, 128 
Tourmaline tongs, 130 
Transparent gems, cutting of, 71 

scratching of, 56 

Transvaal, gems from, 92, 134, 146 
Trap cut, 73 
Trapeze cut, 73 
Treated gems, 247, 265 
Tree agate, 217 
Tremayne, Arthur, 286 
Tremolite-actinolite series, 191 
Triboluminescence, 275 
Tribute of the World spinel, 105 
Triclinic crystals, 18, 22 
Triclinic gems, dichroism in, 44 

effect of light on, 39, 40 
Triclinic system, 17, 22 
Tridymite,' 202 
Triplet, 263 
Tripolite, 229 
Trojan, bust of, 205 
Turkestan, gems from, 174, 190, 

Turquoise, 116, 167, 172 

chemical test for, 14 

color in, importance of, 26 

composition of, 12 

crystallization of, 22 

effect of acid on, 13 

effect of grease on, 13 

imitation, 262 

luster of, 31 


Turquoise, origin of, 69 
resemblance to variscite, 171 
specific gravity test for, 55 
treated, 266 

Turquoise-matrix, 174 

Twin crystals, 16, 17 

Twinning, in gems, 17, 57, 105, 
107, 112, 113, 117, 159, 175, 
180, 181, 196, 205, 207 
parting due to, 60 

Ultralite, 248 
Ultramarine, 183 

Ultraviolet light, 51, 270, 271, 272, 
273, 274, 275, 276, 277, 278, 
' 279, 280, 282 
rock crystal in, 208 
Uneven fracture, 61 
Uniaxial gem, 40 
optic axis in, 41 
Unio, 237 
Union of South Africa, diamond 

cutting in, 95 
diamond from, 88 
United States, diamond cutting in, 


diamond die industry in, 96 

gems from, 90, 113, 116, 139, 

145, 158, 162, 184, 217, 223, 

238; see also names of states 

manufacture of imitations in, 

manufacture of synthetics in, 

250, 255 

United States Bureau of Mines, 90 
United States National Museum, 

115, 207, 227 
Univalve mollusk, 237 
Unruh, Lee M., 72 
Unusual effects of gems, 50 
Upper Burma, gems from, 183, 190 

Ural Mountains, gems from, 90, 
134, 140, 147, 155, 170, 178, 
179, 193, 205, 215; see also 
Russia, Siberia 

Uralian emerald, 147 

Uruguay, gems from, 145, 206, 219 

Use of gems, see War use, Indus- 
trial use 

Utah, gems from, 144, 157, 171 

Utahlite, 172 

Utility magnifier, 27 

Uvarovite, 143 

Value of gems, factors determin- 
ing, 8, 9 

van Berquem, Ludwig, 71 

van Niekirk, Schalk, 76 

Vapor lamp, mercury, 280, 281 

Vargas diamond, 92 

Variscite, 171 

Vegetable gems, 233 

Vegetable products, distinguished 
from minerals, 6 

Venezuela, diamond from, 89, 94 

Venus's-hairstone, 209 

Vermont, idocrase from, 195 

Verneuil, Auguste, 250 

Verneuil furnace, 251 

Vesuvianite, 194 

Vesuvius, Mount, gems from, 117, 
181, 194, 195 

Victoria, Queen, 105, 228 

Vinegar, effect of, on pearl, 13 

Violane, 119 

Virginia, gems from, 173, 179, 197, 

Vitreous luster, 31 

Vitreous silica, 260 

Volcanic rock, gems in, 75, 173, 

Volcano deposits, 65, 77, 87 


von Laue, 23 

von Prehn, Colonel, 184 

Wales, river pearl from, 238 
War use of gems, 95, 96, 130, 143, 

254, 256, 274 

Washing pan, diamond, 81 
Washing plant, diamond, 79 
Water sapphire, 117 
Waxy luster, 31 
Weight, 51 
Wernerite, 117 
Wesselton diamond mine, 78 
Western United States; gems from, 

217, 223 

West Virginia, diamond from, 90 
Whitby jet, 245 
White Cliffs opal field, New South 

Wales, 226 
White opal, 224, 226 
White sapphire, synthetic, 25 U 


Wild, George O., 221 
Willemite, 140 

crystallization of, 21 

luminescence of, 273 
Williamson diamond mine, 88 
Wilson, Ben Hur, 285 
Wind, action of, 67 
Wood, agatized, 222 

jasperized, 222 

opalized, 222 

petrified, 222 

silicified, 222 

turned to jet, 244 
Wyoming, gems from, 192, 217, 
219, 223 

X-ray, 16, 24 
cause of color in smoky quartz, 

for identification of pearl, 269, 


luminescence due to, 270 
of synthetic corundum, 253 
picture of beryl, 24 
sphalerite studied with, 111 

Yellow ground, 77 
Yellowstone National Park, Wyo- 
ming, 231 

Zeberged, olivine from, 138 
Zeolite, 184 
Zinc blende, 111 
Zincite, 141, 274 
Zircon, 148 

absorption spectrum in, 43, 44 

brittleness of, 61 

composition of, 12 

crystallization of, 19, 20, 149 

dichroism in, 45 

double refraction in, 40 

luster of, 31 

occurrence of, 65 

resemblance to diamond, 153 

specific gravity of, 52, 55 

synthetic, 253 

synthetic spinel resembling, 256 

treated, 266 

twin crystal of, 17 
Zodac, Peter, 285 
Zodiacal signs, gems of the, 4, 5 
Zoisite, 148, 195 

jadelike, 200